diff --git a/src/bonsai/bonsai/bim/module/project/operator.py b/src/bonsai/bonsai/bim/module/project/operator.py
index 0650cda238..26850ce85a 100644
--- a/src/bonsai/bonsai/bim/module/project/operator.py
+++ b/src/bonsai/bonsai/bim/module/project/operator.py
@@ -119,6 +119,8 @@ class NewProject(bpy.types.Operator):
             bpy.context.scene.unit_settings.length_unit = "MILLIMETERS"
             bim_props.area_unit = "SQUARE_METRE"
             bim_props.volume_unit = "CUBIC_METRE"
+            bim_props.mass_unit = "KILOGRAM"
+            bim_props.time_unit = "SECOND"
             pprops.template_file = "IFC4 Demo Template.ifc"
 
         if self.preset != "wizard":
diff --git a/src/bonsai/bonsai/bim/module/project/ui.py b/src/bonsai/bonsai/bim/module/project/ui.py
index 6674a1a51a..6fe5b55604 100644
--- a/src/bonsai/bonsai/bim/module/project/ui.py
+++ b/src/bonsai/bonsai/bim/module/project/ui.py
@@ -356,8 +356,23 @@ class BIM_PT_new_project_wizard(Panel):
         row.prop(props, "area_unit", text="Area Unit")
         row = self.layout.row()
         row.prop(props, "volume_unit", text="Volume Unit")
+        row = self.layout.row()
         prop_with_search(self.layout, pprops, "template_file", text="Template")
 
+        if tool.Blender.get_addon_preferences().mass_time_units_in_wizard:
+            header, body = self.layout.panel("Mass and Time Units", default_closed=True)
+            if header:
+                header.label(text="Mass and Time Units")
+            if body:
+                label = "Add Mass and Time Units" if not props.add_mass_time_units else "Remove Mass and Time Units"
+                body.prop(props, "add_mass_time_units", toggle=True, text=label)
+                if props.add_mass_time_units:
+                    row = body.row()
+                    row.prop(props, "mass_unit", text="Mass Unit")
+                    row = body.row()
+                    row.prop(props, "time_unit", text="Time Unit")
+
+        self.layout.use_property_split = True
         row = self.layout.row()
         row.operator("bim.create_project")
 
diff --git a/src/bonsai/bonsai/bim/prop.py b/src/bonsai/bonsai/bim/prop.py
index 7a4464c986..08137a133e 100644
--- a/src/bonsai/bonsai/bim/prop.py
+++ b/src/bonsai/bonsai/bim/prop.py
@@ -586,7 +586,33 @@ class BIMProperties(PropertyGroup):
         ],
         name="IFC Volume Unit",
     )
+    add_mass_time_units: bpy.props.BoolProperty(
+        name="Add Mass and Time Units",
+        description="Enable to define mass and time units for the project",
+        default=False,
+    )
+    mass_unit: EnumProperty(
+        items=[
+            ("KILOGRAM", "Kilogram", "Kilograms"),
+            ("GRAM", "Gram", "Grams"),
+            ("POUND", "Pound", "Pounds"),
+            ("OUNCE", "Ounce", "Ounces"),
+            ("TONNE", "Tonne", "Metric Tons"),
+        ],
+        name="Mass Unit",
+        default="KILOGRAM",
+    )
 
+    time_unit: EnumProperty(
+        items=[
+            ("SECOND", "Second", "Seconds"),
+            ("MINUTE", "Minute", "Minutes"),
+            ("HOUR", "Hour", "Hours"),
+            ("DAY", "Day", "Days"),
+        ],
+        name="Time Unit",
+        default="HOUR",
+    )
     if TYPE_CHECKING:
         is_dirty: bool
         schema_dir: str
@@ -599,6 +625,8 @@ class BIMProperties(PropertyGroup):
         section_line_decorator_width: float
         area_unit: str
         volume_unit: str
+        mass_unit: str
+        time_unit: str
 
 
 class IfcParameter(PropertyGroup):
diff --git a/src/bonsai/bonsai/bim/ui.py b/src/bonsai/bonsai/bim/ui.py
index b7ed2180c1..d41546904c 100644
--- a/src/bonsai/bonsai/bim/ui.py
+++ b/src/bonsai/bonsai/bim/ui.py
@@ -684,6 +684,12 @@ class BIM_ADDON_preferences(bpy.types.AddonPreferences):
         default=False,
     )
 
+    mass_time_units_in_wizard: BoolProperty(
+        name="Mass and time units in project wizard",
+        description="Show mass and time units section in the new project wizard panel",
+        default=False,
+    )
+
     if TYPE_CHECKING:
         svg2pdf_command: str
         svg2dxf_command: str
@@ -720,6 +726,7 @@ class BIM_ADDON_preferences(bpy.types.AddonPreferences):
         doc: DocPreferences
         default_parameters: DefaultParameters
         container_hide_show_isolate: bool
+        mass_time_units_in_wizard: bool
 
     def draw(self, context: bpy.types.Context) -> None:
         layout = self.layout
@@ -901,6 +908,7 @@ class BIM_ADDON_preferences(bpy.types.AddonPreferences):
 
     def draw_extras_settings(self, layout: bpy.types.UILayout, context: bpy.types.Context) -> None:
         layout.prop(self, "container_hide_show_isolate")
+        layout.prop(self, "mass_time_units_in_wizard")
 
 
 # Scene panel groups
diff --git a/src/bonsai/bonsai/core/tool.py b/src/bonsai/bonsai/core/tool.py
index 7fcfd25fde..d8e4dd2396 100644
--- a/src/bonsai/bonsai/core/tool.py
+++ b/src/bonsai/bonsai/core/tool.py
@@ -1123,7 +1123,7 @@ class Unit:
     def set_active_unit(cls, unit): pass
     def get_project_currency_unit(cls): pass
     def get_currency_name(cls): pass
-
+    def add_mass_and_time_units(cls): pass
 
 @interface
 class Voider:
diff --git a/src/bonsai/bonsai/core/unit.py b/src/bonsai/bonsai/core/unit.py
index a075c9c5e5..a4c52508f1 100644
--- a/src/bonsai/bonsai/core/unit.py
+++ b/src/bonsai/bonsai/core/unit.py
@@ -28,20 +28,43 @@ if TYPE_CHECKING:
 
 def assign_scene_units(ifc: type[tool.Ifc], unit: type[tool.Unit]) -> None:
     if unit.is_scene_unit_metric():
-        prefix = unit.get_scene_unit_si_prefix("LENGTHUNIT")
-        lengthunit = ifc.run("unit.add_si_unit", unit_type="LENGTHUNIT", prefix=prefix)
-        prefix = unit.get_scene_unit_si_prefix("AREAUNIT")
-        areaunit = ifc.run("unit.add_si_unit", unit_type="AREAUNIT", prefix=prefix)
-        prefix = unit.get_scene_unit_si_prefix("VOLUMEUNIT")
-        volumeunit = ifc.run("unit.add_si_unit", unit_type="VOLUMEUNIT", prefix=prefix)
+        lengthunit = ifc.run("unit.add_si_unit", unit_type="LENGTHUNIT", prefix=unit.get_scene_unit_si_prefix("LENGTHUNIT"))
+        areaunit = ifc.run("unit.add_si_unit", unit_type="AREAUNIT", prefix=unit.get_scene_unit_si_prefix("AREAUNIT"))
+        volumeunit = ifc.run("unit.add_si_unit", unit_type="VOLUMEUNIT", prefix=unit.get_scene_unit_si_prefix("VOLUMEUNIT"))
+        planeangleunit = ifc.run("unit.add_conversion_based_unit", name="degree")
+        units = [lengthunit, areaunit, volumeunit, planeangleunit]
+
+        if unit.add_mass_and_time_units():
+            prefix = unit.get_scene_unit_si_prefix("MASSUNIT")
+            if prefix == "CONVERSION":
+                massunit = ifc.run("unit.add_conversion_based_unit", name=unit.get_scene_unit_name("MASSUNIT").lower())
+            else:
+                massunit = ifc.run("unit.add_si_unit", unit_type="MASSUNIT", prefix=prefix)
+            prefix = unit.get_scene_unit_si_prefix("TIMEUNIT")
+            if prefix == "CONVERSION":
+                timeunit = ifc.run("unit.add_conversion_based_unit", name=unit.get_scene_unit_name("TIMEUNIT").lower())
+            else:
+                timeunit = ifc.run("unit.add_si_unit", unit_type="TIMEUNIT", prefix=prefix)
+            units += [massunit, timeunit]
+
     else:
         lengthunit = ifc.run("unit.add_conversion_based_unit", name=unit.get_scene_unit_name("LENGTHUNIT"))
         areaunit = ifc.run("unit.add_conversion_based_unit", name=unit.get_scene_unit_name("AREAUNIT"))
         volumeunit = ifc.run("unit.add_conversion_based_unit", name=unit.get_scene_unit_name("VOLUMEUNIT"))
+        planeangleunit = ifc.run("unit.add_conversion_based_unit", name="degree")
+        units = [lengthunit, areaunit, volumeunit, planeangleunit]
 
-    planeangleunit = ifc.run("unit.add_conversion_based_unit", name="degree")
-
-    ifc.run("unit.assign_unit", units=[lengthunit, areaunit, volumeunit, planeangleunit])
+        if unit.add_mass_and_time_units():
+            massunit = ifc.run("unit.add_conversion_based_unit", name=unit.get_scene_unit_name("MASSUNIT").lower())
+            time_unit_name = unit.get_scene_unit_name("TIMEUNIT")
+            if time_unit_name == "SECOND":
+                timeunit = ifc.run("unit.add_si_unit", unit_type="TIMEUNIT", prefix=None)
+            else:
+                timeunit = ifc.run("unit.add_conversion_based_unit", name=time_unit_name.lower())
+            units += [massunit, timeunit]
+    print("Add mass and time units:", unit.add_mass_and_time_units())
+    print("Assigning units:", units)
+    ifc.run("unit.assign_unit", units=units)
 
 
 def assign_unit(ifc: type[tool.Ifc], unit_tool: type[tool.Unit], unit: ifcopenshell.entity_instance) -> None:
diff --git a/src/bonsai/bonsai/tool/unit.py b/src/bonsai/bonsai/tool/unit.py
index d01d51f3cb..c982c43523 100644
--- a/src/bonsai/bonsai/tool/unit.py
+++ b/src/bonsai/bonsai/tool/unit.py
@@ -266,7 +266,7 @@ def parse_distance_string(input_string: str, use_project_unit: bool = True) -> t
 
 
 class Unit(bonsai.core.tool.Unit):
-    UNIT_TYPE = Literal["LENGTHUNIT", "AREAUNIT", "VOLUMEUNIT"]
+    UNIT_TYPE = Literal["LENGTHUNIT", "AREAUNIT", "VOLUMEUNIT", "MASSUNIT", "TIMEUNIT"]
 
     @staticmethod
     def format_distance(meters: float, use_imperial: bool = None, **kwargs) -> str:
@@ -343,6 +343,10 @@ class Unit(bonsai.core.tool.Unit):
             return bim_props.area_unit
         elif unit_type == "VOLUMEUNIT":
             return bim_props.volume_unit
+        elif unit_type == "MASSUNIT":
+            return bim_props.mass_unit.lower()
+        elif unit_type == "TIMEUNIT":
+            return bim_props.time_unit.lower()
         else:
             assert_never(unit_type)
 
@@ -359,6 +363,24 @@ class Unit(bonsai.core.tool.Unit):
             unit = bim_props.area_unit
         elif unit_type == "VOLUMEUNIT":
             unit = bim_props.volume_unit
+        elif unit_type == "MASSUNIT":
+            unit = bim_props.mass_unit
+            if unit == "GRAM":
+                return None
+            elif unit == "KILOGRAM":
+                return "KILO"
+            elif unit == "TONNE":
+                return "MEGA"
+            elif unit in ["POUND", "OUNCE"]:
+                return "CONVERSION"
+            else:
+                return None
+        elif unit_type == "TIMEUNIT":
+            unit = bim_props.time_unit
+            if unit == "SECOND":
+                return None
+            else:
+                return "CONVERSION"
         else:
             assert_never(unit_type)
         if "/" in unit:
@@ -477,3 +499,9 @@ class Unit(bonsai.core.tool.Unit):
         elif ifc_class == "IfcMonetaryUnit":
             return "COPY_ID"
         return "MOD_MESHDEFORM"
+
+    @classmethod
+    def add_mass_and_time_units(cls) -> bool:
+        """Return True if the user wants to add mass and time units, False otherwise."""
+        bim_props = tool.Blender.get_bim_props()
+        return getattr(bim_props, "add_mass_time_units", False)
diff --git a/src/bonsai/test/core/test_unit.py b/src/bonsai/test/core/test_unit.py
index d79b6b83fb..2bbd783cc3 100644
--- a/src/bonsai/test/core/test_unit.py
+++ b/src/bonsai/test/core/test_unit.py
@@ -26,38 +26,119 @@ class TestAssignSceneUnits:
         unit.get_scene_unit_si_prefix("LENGTHUNIT").should_be_called().will_return("prefix")
         unit.get_scene_unit_si_prefix("AREAUNIT").should_be_called().will_return("prefix")
         unit.get_scene_unit_si_prefix("VOLUMEUNIT").should_be_called().will_return("prefix")
+        unit.add_mass_and_time_units().should_be_called().will_return(True)
+        unit.get_scene_unit_si_prefix("MASSUNIT").should_be_called().will_return("KILO")
+        unit.get_scene_unit_si_prefix("TIMEUNIT").should_be_called().will_return(None)
+
         ifc.run("unit.add_si_unit", unit_type="LENGTHUNIT", prefix="prefix").should_be_called().will_return(
             "lengthunit"
         )
-
         ifc.run("unit.add_si_unit", unit_type="AREAUNIT", prefix="prefix").should_be_called().will_return("areaunit")
-
         ifc.run("unit.add_si_unit", unit_type="VOLUMEUNIT", prefix="prefix").should_be_called().will_return(
             "volumeunit"
         )
-
+        ifc.run("unit.add_si_unit", unit_type="MASSUNIT", prefix="KILO").should_be_called().will_return("massunit")
+        ifc.run("unit.add_si_unit", unit_type="TIMEUNIT", prefix=None).should_be_called().will_return("timeunit")
         ifc.run("unit.add_conversion_based_unit", name="degree").should_be_called().will_return("planeangleunit")
 
+        ifc.run(
+            "unit.assign_unit", units=["lengthunit", "areaunit", "volumeunit", "planeangleunit", "massunit", "timeunit"]
+        ).should_be_called()
+        subject.assign_scene_units(ifc, unit)
+
+    def test_creating_and_assigning_metric_units_without_mass_and_time(self, ifc, unit):
+        unit.is_scene_unit_metric().should_be_called().will_return(True)
+        unit.get_scene_unit_si_prefix("LENGTHUNIT").should_be_called().will_return("CENTI")
+        unit.get_scene_unit_si_prefix("AREAUNIT").should_be_called().will_return("CENTI")
+        unit.get_scene_unit_si_prefix("VOLUMEUNIT").should_be_called().will_return("CENTI")
+        unit.add_mass_and_time_units().should_be_called().will_return(False)
+        ifc.run("unit.add_si_unit", unit_type="LENGTHUNIT", prefix="CENTI").should_be_called().will_return("lengthunit")
+        ifc.run("unit.add_si_unit", unit_type="AREAUNIT", prefix="CENTI").should_be_called().will_return("areaunit")
+        ifc.run("unit.add_si_unit", unit_type="VOLUMEUNIT", prefix="CENTI").should_be_called().will_return("volumeunit")
+        ifc.run("unit.add_conversion_based_unit", name="degree").should_be_called().will_return("planeangleunit")
         ifc.run("unit.assign_unit", units=["lengthunit", "areaunit", "volumeunit", "planeangleunit"]).should_be_called()
         subject.assign_scene_units(ifc, unit)
 
     def test_creating_and_assigning_imperial_units(self, ifc, unit):
         unit.is_scene_unit_metric().should_be_called().will_return(False)
-        unit.get_scene_unit_name("LENGTHUNIT").should_be_called().will_return("lengthname")
-        ifc.run("unit.add_conversion_based_unit", name="lengthname").should_be_called().will_return("lengthunit")
-
-        unit.get_scene_unit_name("AREAUNIT").should_be_called().will_return("areaname")
-        ifc.run("unit.add_conversion_based_unit", name="areaname").should_be_called().will_return("areaunit")
-
-        unit.get_scene_unit_name("VOLUMEUNIT").should_be_called().will_return("volumename")
-        ifc.run("unit.add_conversion_based_unit", name="volumename").should_be_called().will_return("volumeunit")
+        unit.get_scene_unit_name("LENGTHUNIT").should_be_called().will_return("foot")
+        unit.get_scene_unit_name("AREAUNIT").should_be_called().will_return("square foot")
+        unit.get_scene_unit_name("VOLUMEUNIT").should_be_called().will_return("cubic foot")
+        unit.add_mass_and_time_units().should_be_called().will_return(True)
+        unit.get_scene_unit_name("MASSUNIT").should_be_called().will_return("pound")
+        unit.get_scene_unit_name("TIMEUNIT").should_be_called().will_return("SECOND")
 
+        ifc.run("unit.add_conversion_based_unit", name="foot").should_be_called().will_return("lengthunit")
+        ifc.run("unit.add_conversion_based_unit", name="square foot").should_be_called().will_return("areaunit")
+        ifc.run("unit.add_conversion_based_unit", name="cubic foot").should_be_called().will_return("volumeunit")
+        ifc.run("unit.add_conversion_based_unit", name="pound").should_be_called().will_return("massunit")
+        ifc.run("unit.add_si_unit", unit_type="TIMEUNIT", prefix=None).should_be_called().will_return("timeunit")
         ifc.run("unit.add_conversion_based_unit", name="degree").should_be_called().will_return("planeangleunit")
 
+        ifc.run(
+            "unit.assign_unit", units=["lengthunit", "areaunit", "volumeunit", "planeangleunit", "massunit", "timeunit"]
+        ).should_be_called()
+        subject.assign_scene_units(ifc, unit)
+
+    def test_creating_and_assigning_imperial_units_without_mass_and_time(self, ifc, unit):
+        unit.is_scene_unit_metric().should_be_called().will_return(False)
+        unit.get_scene_unit_name("LENGTHUNIT").should_be_called().will_return("yard")
+        unit.get_scene_unit_name("AREAUNIT").should_be_called().will_return("square yard")
+        unit.get_scene_unit_name("VOLUMEUNIT").should_be_called().will_return("cubic yard")
+        unit.add_mass_and_time_units().should_be_called().will_return(False)
+        ifc.run("unit.add_conversion_based_unit", name="yard").should_be_called().will_return("lengthunit")
+        ifc.run("unit.add_conversion_based_unit", name="square yard").should_be_called().will_return("areaunit")
+        ifc.run("unit.add_conversion_based_unit", name="cubic yard").should_be_called().will_return("volumeunit")
+        ifc.run("unit.add_conversion_based_unit", name="degree").should_be_called().will_return("planeangleunit")
         ifc.run("unit.assign_unit", units=["lengthunit", "areaunit", "volumeunit", "planeangleunit"]).should_be_called()
         subject.assign_scene_units(ifc, unit)
 
 
+    def test_creating_metric_units_with_conversion_based_mass_and_time(self, ifc, unit):
+        unit.is_scene_unit_metric().should_be_called().will_return(True)
+        unit.get_scene_unit_si_prefix("LENGTHUNIT").should_be_called().will_return("MILLI")
+        unit.get_scene_unit_si_prefix("AREAUNIT").should_be_called().will_return(None)
+        unit.get_scene_unit_si_prefix("VOLUMEUNIT").should_be_called().will_return(None)
+        unit.add_mass_and_time_units().should_be_called().will_return(True)
+        unit.get_scene_unit_si_prefix("MASSUNIT").should_be_called().will_return("CONVERSION")
+        unit.get_scene_unit_name("MASSUNIT").should_be_called().will_return("tonne")
+        unit.get_scene_unit_si_prefix("TIMEUNIT").should_be_called().will_return("CONVERSION")
+        unit.get_scene_unit_name("TIMEUNIT").should_be_called().will_return("minute")
+
+        ifc.run("unit.add_si_unit", unit_type="LENGTHUNIT", prefix="MILLI").should_be_called().will_return("lengthunit")
+        ifc.run("unit.add_si_unit", unit_type="AREAUNIT", prefix=None).should_be_called().will_return("areaunit")
+        ifc.run("unit.add_si_unit", unit_type="VOLUMEUNIT", prefix=None).should_be_called().will_return("volumeunit")
+        ifc.run("unit.add_conversion_based_unit", name="tonne").should_be_called().will_return("massunit")
+        ifc.run("unit.add_conversion_based_unit", name="minute").should_be_called().will_return("timeunit")
+        ifc.run("unit.add_conversion_based_unit", name="degree").should_be_called().will_return("planeangleunit")
+
+        ifc.run(
+            "unit.assign_unit", units=["lengthunit", "areaunit", "volumeunit", "planeangleunit", "massunit", "timeunit"]
+        ).should_be_called()
+        subject.assign_scene_units(ifc, unit)
+
+    def test_creating_imperial_units_with_conversion_based_units(self, ifc, unit):
+        unit.is_scene_unit_metric().should_be_called().will_return(False)
+        unit.get_scene_unit_name("LENGTHUNIT").should_be_called().will_return("inch")
+        unit.get_scene_unit_name("AREAUNIT").should_be_called().will_return("square inch")
+        unit.get_scene_unit_name("VOLUMEUNIT").should_be_called().will_return("cubic inch")
+        unit.add_mass_and_time_units().should_be_called().will_return(True)
+        unit.get_scene_unit_name("MASSUNIT").should_be_called().will_return("ounce")
+        unit.get_scene_unit_name("TIMEUNIT").should_be_called().will_return("hour")
+
+        ifc.run("unit.add_conversion_based_unit", name="inch").should_be_called().will_return("lengthunit")
+        ifc.run("unit.add_conversion_based_unit", name="square inch").should_be_called().will_return("areaunit")
+        ifc.run("unit.add_conversion_based_unit", name="cubic inch").should_be_called().will_return("volumeunit")
+        ifc.run("unit.add_conversion_based_unit", name="ounce").should_be_called().will_return("massunit")
+        ifc.run("unit.add_conversion_based_unit", name="hour").should_be_called().will_return("timeunit")
+        ifc.run("unit.add_conversion_based_unit", name="degree").should_be_called().will_return("planeangleunit")
+
+        ifc.run(
+            "unit.assign_unit", units=["lengthunit", "areaunit", "volumeunit", "planeangleunit", "massunit", "timeunit"]
+        ).should_be_called()
+        subject.assign_scene_units(ifc, unit)
+
+
 class TestAssignUnit:
     def test_run(self, ifc, unit):
         ifc.run("unit.assign_unit", units=["unit"]).should_be_called()
diff --git a/src/bonsai/test/tool/test_unit.py b/src/bonsai/test/tool/test_unit.py
index 212c72a559..190a8fa302 100644
--- a/src/bonsai/test/tool/test_unit.py
+++ b/src/bonsai/test/tool/test_unit.py
@@ -135,6 +135,35 @@ class TestGetSceneUnitName(NewFile):
         bpy.context.scene.unit_settings.system = "NONE"
         assert subject.get_scene_unit_name("LENGTHUNIT") == "foot"
 
+    def test_getting_mass_unit_names(self):
+        """Test getting mass unit names for different systems"""
+        assert bpy.context.scene
+        props = tool.Blender.get_bim_props()
+        props.mass_unit = "GRAM"
+        assert subject.get_scene_unit_name("MASSUNIT") == "gram"
+        props.mass_unit = "KILOGRAM"
+        assert subject.get_scene_unit_name("MASSUNIT") == "kilogram"
+        props.mass_unit = "POUND"
+        assert subject.get_scene_unit_name("MASSUNIT") == "pound"
+        props.mass_unit = "OUNCE"
+        assert subject.get_scene_unit_name("MASSUNIT") == "ounce"
+        props.mass_unit = "TONNE"
+        assert subject.get_scene_unit_name("MASSUNIT") == "tonne"
+
+    def test_getting_time_unit_names(self):
+        """Test getting time unit names for different systems"""
+        assert bpy.context.scene
+        props = tool.Blender.get_bim_props()
+
+        props.time_unit = "SECOND"
+        assert subject.get_scene_unit_name("TIMEUNIT") == "second"
+        props.time_unit = "MINUTE"
+        assert subject.get_scene_unit_name("TIMEUNIT") == "minute"
+        props.time_unit = "HOUR"
+        assert subject.get_scene_unit_name("TIMEUNIT") == "hour"
+        props.time_unit = "DAY"
+        assert subject.get_scene_unit_name("TIMEUNIT") == "day"
+
 
 class TestGetSceneUnitSIPrefix:
     def test_run(self):
@@ -162,6 +191,30 @@ class TestGetSceneUnitSIPrefix:
         props.volume_unit = "MILLI/CUBIC_METRE"
         assert subject.get_scene_unit_si_prefix("VOLUMEUNIT") == "MILLI"
 
+    def test_mass_and_time_unit_prefixes(self):
+        assert bpy.context.scene
+        props = tool.Blender.get_bim_props()
+
+        props.mass_unit = "KILOGRAM"
+        assert subject.get_scene_unit_si_prefix("MASSUNIT") == "KILO"
+        props.mass_unit = "GRAM"
+        assert subject.get_scene_unit_si_prefix("MASSUNIT") is None
+        props.mass_unit = "POUND"
+        assert subject.get_scene_unit_si_prefix("MASSUNIT") == "CONVERSION"
+        props.mass_unit = "OUNCE"
+        assert subject.get_scene_unit_si_prefix("MASSUNIT") == "CONVERSION"
+        props.mass_unit = "TONNE"
+        assert subject.get_scene_unit_si_prefix("MASSUNIT") == "MEGA"
+
+        props.time_unit = "SECOND"
+        assert subject.get_scene_unit_si_prefix("TIMEUNIT") is None
+        props.time_unit = "MINUTE"
+        assert subject.get_scene_unit_si_prefix("TIMEUNIT") == "CONVERSION"
+        props.time_unit = "HOUR"
+        assert subject.get_scene_unit_si_prefix("TIMEUNIT") == "CONVERSION"
+        props.time_unit = "DAY"
+        assert subject.get_scene_unit_si_prefix("TIMEUNIT") == "CONVERSION"
+
 
 class TestImportUnitAttributes(NewFile):
     def test_importing_derived_units(self):
@@ -298,6 +351,96 @@ class TestImportUnits(NewFile):
         assert props.units[5].unit_type == unit6.UnitType
         assert props.units[5].ifc_class == unit6.is_a()
 
+    def test_importing_mass_and_time_units(self):
+        """Test importing mass and time conversion based units"""
+        ifc = ifcopenshell.api.project.create_file()
+        tool.Ifc.set(ifc)
+
+        tonne_unit = ifcopenshell.api.unit.add_conversion_based_unit(ifc, name="tonne")
+        pound_unit = ifcopenshell.api.unit.add_conversion_based_unit(ifc, name="pound")
+        ounce_unit = ifcopenshell.api.unit.add_conversion_based_unit(ifc, name="ounce")
+
+        minute_unit = ifcopenshell.api.unit.add_conversion_based_unit(ifc, name="minute")
+        hour_unit = ifcopenshell.api.unit.add_conversion_based_unit(ifc, name="hour")
+        day_unit = ifcopenshell.api.unit.add_conversion_based_unit(ifc, name="day")
+
+        kg_unit = ifcopenshell.api.unit.add_si_unit(ifc, unit_type="MASSUNIT", prefix="KILO")
+        gram_unit = ifcopenshell.api.unit.add_si_unit(ifc, unit_type="MASSUNIT")
+        second_unit = ifcopenshell.api.unit.add_si_unit(ifc, unit_type="TIMEUNIT")
+
+        ifcopenshell.api.root.create_entity(ifc, ifc_class="IfcProject")
+        ifcopenshell.api.unit.assign_unit(ifc, units=[tonne_unit, minute_unit, kg_unit])
+
+        subject.import_units()
+        props = tool.Unit.get_unit_props()
+
+        assert len(props.units) == 15
+
+        unit_ids = [u.ifc_definition_id for u in props.units]
+        assert tonne_unit.id() in unit_ids
+        assert pound_unit.id() in unit_ids
+        assert ounce_unit.id() in unit_ids
+        assert minute_unit.id() in unit_ids
+        assert hour_unit.id() in unit_ids
+        assert day_unit.id() in unit_ids
+        assert kg_unit.id() in unit_ids
+        assert gram_unit.id() in unit_ids
+        assert second_unit.id() in unit_ids
+
+        tonne_prop = next(u for u in props.units if u.ifc_definition_id == tonne_unit.id())
+        assert tonne_prop.name == "tonne"
+        assert tonne_prop.unit_type == "MASSUNIT"
+        assert tonne_prop.is_assigned is True
+        assert tonne_prop.ifc_class == "IfcConversionBasedUnit"
+
+        pound_prop = next(u for u in props.units if u.ifc_definition_id == pound_unit.id())
+        assert pound_prop.name == "pound"
+        assert pound_prop.unit_type == "MASSUNIT"
+        assert pound_prop.is_assigned is False
+        assert pound_prop.ifc_class == "IfcConversionBasedUnit"
+
+        ounce_prop = next(u for u in props.units if u.ifc_definition_id == ounce_unit.id())
+        assert ounce_prop.name == "ounce"
+        assert ounce_prop.unit_type == "MASSUNIT"
+        assert ounce_prop.is_assigned is False
+        assert ounce_prop.ifc_class == "IfcConversionBasedUnit"
+
+        kg_prop = next(u for u in props.units if u.ifc_definition_id == kg_unit.id())
+        assert kg_prop.name == "KILOGRAM"
+        assert kg_prop.unit_type == "MASSUNIT"
+        assert kg_prop.is_assigned is True
+        assert kg_prop.ifc_class == "IfcSIUnit"
+
+        gram_prop = next(u for u in props.units if u.ifc_definition_id == gram_unit.id())
+        assert gram_prop.name == "GRAM"
+        assert gram_prop.unit_type == "MASSUNIT"
+        assert gram_prop.is_assigned is False
+        assert gram_prop.ifc_class == "IfcSIUnit"
+
+        minute_prop = next(u for u in props.units if u.ifc_definition_id == minute_unit.id())
+        assert minute_prop.name == "minute"
+        assert minute_prop.unit_type == "TIMEUNIT"
+        assert minute_prop.is_assigned is True
+        assert minute_prop.ifc_class == "IfcConversionBasedUnit"
+
+        hour_prop = next(u for u in props.units if u.ifc_definition_id == hour_unit.id())
+        assert hour_prop.name == "hour"
+        assert hour_prop.unit_type == "TIMEUNIT"
+        assert hour_prop.is_assigned is False
+        assert hour_prop.ifc_class == "IfcConversionBasedUnit"
+
+        day_prop = next(u for u in props.units if u.ifc_definition_id == day_unit.id())
+        assert day_prop.name == "day"
+        assert day_prop.unit_type == "TIMEUNIT"
+        assert day_prop.is_assigned is False
+        assert day_prop.ifc_class == "IfcConversionBasedUnit"
+
+        second_prop = next(u for u in props.units if u.ifc_definition_id == second_unit.id())
+        assert second_prop.name == "SECOND"
+        assert second_prop.unit_type == "TIMEUNIT"
+        assert second_prop.is_assigned is False
+        assert second_prop.ifc_class == "IfcSIUnit"
+
 
 class TestIsSceneUnitMetric(NewFile):
     def test_run(self):
diff --git a/src/ifcopenshell-python/ifcopenshell/api/unit/add_conversion_based_unit.py b/src/ifcopenshell-python/ifcopenshell/api/unit/add_conversion_based_unit.py
index bb1e920257..6a4f17f8fd 100644
--- a/src/ifcopenshell-python/ifcopenshell/api/unit/add_conversion_based_unit.py
+++ b/src/ifcopenshell-python/ifcopenshell/api/unit/add_conversion_based_unit.py
@@ -32,7 +32,7 @@ def add_conversion_based_unit(
     function. You can choose from one of: inch, foot, yard, mile, square
     inch, square foot, square yard, acre, square mile, cubic inch, cubic
     foot, cubic yard, litre, fluid ounce UK, fluid ounce US, pint UK, pint
-    US, gallon UK, gallon US, degree, ounce, pound, ton UK, ton US, lbf,
+    US, gallon UK, gallon US, degree, ounce, pound, ton UK, ton US, tonne, lbf,
     kip, psi, ksi, minute, hour, day, btu, and fahrenheit.
 
     :param name: A converted name chosen from the list above.
@@ -61,7 +61,11 @@ def add_conversion_based_unit(
     dimensions = ifcopenshell.util.unit.named_dimensions[unit_type]
     exponents = file.createIfcDimensionalExponents(*dimensions)
     si_name = ifcopenshell.util.unit.si_type_names[unit_type]
-    si_unit = file.createIfcSIUnit(UnitType=unit_type, Name=si_name)
+
+    if unit_type == "MASSUNIT":
+        si_unit = file.createIfcSIUnit(UnitType=unit_type, Name=si_name, Prefix="KILO")
+    else:
+        si_unit = file.createIfcSIUnit(UnitType=unit_type, Name=si_name)
 
     conversion_real = ifcopenshell.util.unit.si_conversions.get(name, 1)
     value_component = file.create_entity("IfcReal", **{"wrappedValue": conversion_real})
diff --git a/src/ifcopenshell-python/ifcopenshell/api/unit/assign_unit.py b/src/ifcopenshell-python/ifcopenshell/api/unit/assign_unit.py
index d57acbd435..5861e4248a 100644
--- a/src/ifcopenshell-python/ifcopenshell/api/unit/assign_unit.py
+++ b/src/ifcopenshell-python/ifcopenshell/api/unit/assign_unit.py
@@ -55,8 +55,12 @@ def assign_unit(
         length = ifcopenshell.api.unit.add_si_unit(model, unit_type="LENGTHUNIT", prefix="MILLI")
         area = ifcopenshell.api.unit.add_si_unit(model, unit_type="AREAUNIT")
 
-        # Make it our default units, if we are doing a metric building
-        ifcopenshell.api.unit.assign_unit(model, units=[length, area])
+        # Optionally, add mass and time units
+        mass = ifcopenshell.api.unit.add_si_unit(model, unit_type="MASSUNIT", prefix="KILO")
+        time = ifcopenshell.api.unit.add_si_unit(model, unit_type="TIMEUNIT")
+
+        # Make these the default units for the project
+        ifcopenshell.api.unit.assign_unit(model, units=[length, area, mass, time])
 
         # Alternatively, you may specify without any arguments to
         # automatically create millimeters, square meters, and cubic meters
@@ -139,6 +143,7 @@ class Usecase:
         elif unit_type == "volume":
             dimensional_exponents = self.file.createIfcDimensionalExponents(3, 0, 0, 0, 0, 0, 0)
             name_prefix = "cubic"
+
         si_unit = self.file.createIfcSIUnit(
             None,
             "{}UNIT".format(unit_type.upper()),
diff --git a/src/ifcopenshell-python/ifcopenshell/util/unit.py b/src/ifcopenshell-python/ifcopenshell/util/unit.py
index cc767fe3a7..86254cb826 100644
--- a/src/ifcopenshell-python/ifcopenshell/util/unit.py
+++ b/src/ifcopenshell-python/ifcopenshell/util/unit.py
@@ -209,6 +209,7 @@ si_conversions = {
     "pound": 0.454,
     "ton UK": 1016.0469088,
     "ton US": 907.18474,
+    "tonne": 1000.0,
     "lbf": 4.4482216153,
     "kip": 4448.2216153,
     "psi": 6894.7572932,
@@ -253,6 +254,7 @@ imperial_types = {
     "pound": "MASSUNIT",
     "ton UK": "MASSUNIT",
     "ton US": "MASSUNIT",
+    "tonne": "MASSUNIT",
     "lbf": "FORCEUNIT",
     "kip": "FORCEUNIT",
     "psi": "PRESSUREUNIT",
@@ -323,6 +325,7 @@ unit_symbols = {
     "pound": "lb",
     "ton UK": "ton",
     "ton US": "ton",
+    "tonne": "t",
     "lbf": "lbf",
     "kip": "kip",
     "psi": "psi",
diff --git a/src/ifcopenshell-python/test/api/unit/test_add_conversion_based_unit.py b/src/ifcopenshell-python/test/api/unit/test_add_conversion_based_unit.py
index 03a8a7edfd..a29b9b2ad8 100644
--- a/src/ifcopenshell-python/test/api/unit/test_add_conversion_based_unit.py
+++ b/src/ifcopenshell-python/test/api/unit/test_add_conversion_based_unit.py
@@ -40,6 +40,54 @@ class TestAddConversionBasedUnitIFC2X3(test.bootstrap.IFC2X3):
         assert si_unit.Prefix is None
         assert si_unit.Name == "METRE"
 
+    def test_adding_mass_units_creates_proper_massunit(self):
+        mass_units = [
+            ("tonne", 1000.0),
+            ("pound", 0.454),
+            ("ounce", 0.02835),
+            ("ton UK", 1016.0469088),
+            ("ton US", 907.18474),
+        ]
+
+        for name, expected_conversion in mass_units:
+            unit = ifcopenshell.api.unit.add_conversion_based_unit(self.file, name=name)
+
+            assert unit.is_a("IfcConversionBasedUnit")
+            assert unit.UnitType == "MASSUNIT"
+            assert unit.Name == name
+
+            actual_conversion = unit.ConversionFactor.ValueComponent.wrappedValue
+            assert actual_conversion == expected_conversion
+
+            target_unit = unit.ConversionFactor.UnitComponent
+            assert target_unit.is_a("IfcSIUnit")
+            assert target_unit.UnitType == "MASSUNIT"
+            assert target_unit.Name == "GRAM"
+            assert target_unit.Prefix == "KILO"
+
+    def test_adding_time_units_creates_proper_timeunit(self):
+        time_units = [
+            ("minute", 60),
+            ("hour", 3600),
+            ("day", 86400),
+        ]
+
+        for name, expected_conversion in time_units:
+            unit = ifcopenshell.api.unit.add_conversion_based_unit(self.file, name=name)
+
+            assert unit.is_a("IfcConversionBasedUnit")
+            assert unit.UnitType == "TIMEUNIT"
+            assert unit.Name == name
+
+            actual_conversion = unit.ConversionFactor.ValueComponent.wrappedValue
+            assert actual_conversion == expected_conversion
+
+            target_unit = unit.ConversionFactor.UnitComponent
+            assert target_unit.is_a("IfcSIUnit")
+            assert target_unit.UnitType == "TIMEUNIT"
+            assert target_unit.Name == "SECOND"
+            assert target_unit.Prefix is None
+
 
 class TestAddConversionBasedUnitIFC4(test.bootstrap.IFC4, TestAddConversionBasedUnitIFC2X3):
     def test_adding_a_unit_with_offset(self):
@@ -61,3 +109,8 @@ class TestAddConversionBasedUnitIFC4(test.bootstrap.IFC4, TestAddConversionBased
         assert si_unit.Prefix is None
         assert si_unit.Name == "KELVIN"
         assert unit.ConversionOffset == -459.67
+
+    def test_unknown_units_fall_back_to_userdefined(self):
+        unknown_unit = ifcopenshell.api.unit.add_conversion_based_unit(self.file, name="unknown_unit")
+        assert unknown_unit.UnitType == "USERDEFINED"
+        assert unknown_unit.Name == "unknown_unit"