diff --git a/src/bonsai/bonsai/bim/prop.py b/src/bonsai/bonsai/bim/prop.py
index eeea68eab9..93730b475b 100644
--- a/src/bonsai/bonsai/bim/prop.py
+++ b/src/bonsai/bonsai/bim/prop.py
@@ -590,7 +590,7 @@ class BIMProperties(PropertyGroup):
         items=[
             ("KILOGRAM", "Kilogram", "Kilograms"),
             ("GRAM", "Gram", "Grams"),
-            ("POUND", "Pound (Mass)", "Pounds"),
+            ("POUND", "Pound", "Pounds"),
             ("OUNCE", "Ounce", "Ounces"),
             ("TON", "Ton", "Metric Tons"),
         ],
diff --git a/src/bonsai/bonsai/core/unit.py b/src/bonsai/bonsai/core/unit.py
index 8517343b37..2e8e627cb7 100644
--- a/src/bonsai/bonsai/core/unit.py
+++ b/src/bonsai/bonsai/core/unit.py
@@ -52,8 +52,13 @@ def assign_scene_units(ifc: type[tool.Ifc], unit: type[tool.Unit]) -> None:
         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"))
-        massunit = ifc.run("unit.add_conversion_based_unit", name=unit.get_scene_unit_name("MASSUNIT"))
-        timeunit = ifc.run("unit.add_conversion_based_unit", name=unit.get_scene_unit_name("TIMEUNIT"))
+        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())
 
     planeangleunit = ifc.run("unit.add_conversion_based_unit", name="degree")
     ifc.run("unit.assign_unit", units=[lengthunit, areaunit, volumeunit, planeangleunit, massunit, timeunit])
diff --git a/src/bonsai/bonsai/tool/unit.py b/src/bonsai/bonsai/tool/unit.py
index b18cb6ff09..293136fb8c 100644
--- a/src/bonsai/bonsai/tool/unit.py
+++ b/src/bonsai/bonsai/tool/unit.py
@@ -365,24 +365,22 @@ class Unit(bonsai.core.tool.Unit):
             unit = bim_props.volume_unit
         elif unit_type == "MASSUNIT":
             unit = bim_props.mass_unit
-            if unit == "KILOGRAM":
-                return "KILO"
-            elif unit == "GRAM":
+            if unit == "GRAM":
                 return None
+            elif unit == "KILOGRAM":
+                return "KILO"
             elif unit == "TON":
                 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:
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..51aa200810 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
@@ -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})