diff --git a/src/bonsai/bonsai/bim/helper.py b/src/bonsai/bonsai/bim/helper.py
index 18e01a5161..d00f7222fa 100644
--- a/src/bonsai/bonsai/bim/helper.py
+++ b/src/bonsai/bonsai/bim/helper.py
@@ -238,7 +238,6 @@ def import_attribute(
     elif data_type == "float":
         measure_class = attribute.type_of_attribute().declared_type().name()
         new.special_type = tool.Pset.get_special_type_for_measure_class(measure_class)
-        new.unit_symbol = tool.Pset.get_unit_symbol_for_special_type(new.special_type, tool.Ifc.get())
         new.float_value = 0.0 if new.is_null else float(data[attribute.name()])
     elif data_type == "enum":
         attribute_type = attribute.type_of_attribute()
diff --git a/src/bonsai/bonsai/bim/module/qto/operator.py b/src/bonsai/bonsai/bim/module/qto/operator.py
index 6aa10c9beb..39cdb9a6ce 100644
--- a/src/bonsai/bonsai/bim/module/qto/operator.py
+++ b/src/bonsai/bonsai/bim/module/qto/operator.py
@@ -151,7 +151,7 @@ class CalculateSingleQuantity(bpy.types.Operator, tool.Ifc.Operator):
         ifc_file = tool.Ifc.get()
         with Profiler("Quantify function time:"):
             results = ifc5d.qto.quantify(ifc_file, elements, rules)
-        ifc5d.qto.edit_qtos(ifc_file, results)
+        ifc5d.qto.edit_qtos(ifc_file, results, target_units=tool.Qto.get_target_units(), rules=rules)
 
         not_quantified_elements = elements - set(results.keys())
         not_quantified_message = tool.Qto.get_not_quantified_elements_message(not_quantified_elements)
@@ -194,7 +194,7 @@ class PerformQuantityTakeOff(bpy.types.Operator, tool.Ifc.Operator):
             ifc_file = tool.Ifc.get()
             with Profiler("Quantify function time:"):
                 results = ifc5d.qto.quantify(ifc_file, elements, rules)
-            ifc5d.qto.edit_qtos(ifc_file, results)
+            ifc5d.qto.edit_qtos(ifc_file, results, target_units=tool.Qto.get_target_units(), rules=rules)
             not_quantified_elements = elements - set(results.keys())
             return not_quantified_elements
 
diff --git a/src/bonsai/bonsai/bim/module/qto/prop.py b/src/bonsai/bonsai/bim/module/qto/prop.py
index 7ffbfcdfa7..adf1f7a2be 100644
--- a/src/bonsai/bonsai/bim/module/qto/prop.py
+++ b/src/bonsai/bonsai/bim/module/qto/prop.py
@@ -27,10 +27,28 @@ from bpy.props import (
 )
 from bpy.types import PropertyGroup
 
+import bonsai.bim.prop
 import bonsai.tool as tool
 
 CALCULATOR_FUNCTION_ENUM_ITEMS: list[Union[tuple[str, str, str], None]] = []
 
+# Measure class (matching ifc5d.qto's Function.measure / SI2ProjectUnitConverter.project_units'
+# keys) -> (BIMQtoProperties field name, tool.Pset special_type, UI label).
+MEASURE_TO_TARGET_UNIT_FIELD: dict[str, tuple[str, str, str]] = {
+    "IfcLengthMeasure": ("target_unit_length", "LENGTH", "Length"),
+    "IfcAreaMeasure": ("target_unit_area", "AREA", "Area"),
+    "IfcVolumeMeasure": ("target_unit_volume", "VOLUME", "Volume"),
+    "IfcMassMeasure": ("target_unit_mass", "MASS", "Mass"),
+    "IfcTimeMeasure": ("target_unit_time", "TIME", "Time"),
+}
+
+
+def _target_unit_items(special_type: str):
+    def getter(self: "BIMQtoProperties", context: bpy.types.Context) -> tool.Blender.BLENDER_ENUM_ITEMS:
+        return bonsai.bim.prop.get_unit_enum_items_for_special_type(special_type, tool.Ifc.get())
+
+    return getter
+
 
 def get_qto_rule(self: "BIMQtoProperties", context: bpy.types.Context) -> list[tuple[str, str, str]]:
     results: list[tuple[str, str, str]] = []
@@ -92,6 +110,11 @@ class BIMQtoProperties(PropertyGroup):
         ),
         default=False,
     )
+    target_unit_length: EnumProperty(items=_target_unit_items("LENGTH"), name="Length Unit")
+    target_unit_area: EnumProperty(items=_target_unit_items("AREA"), name="Area Unit")
+    target_unit_volume: EnumProperty(items=_target_unit_items("VOLUME"), name="Volume Unit")
+    target_unit_mass: EnumProperty(items=_target_unit_items("MASS"), name="Mass Unit")
+    target_unit_time: EnumProperty(items=_target_unit_items("TIME"), name="Time Unit")
 
     if TYPE_CHECKING:
         qto_rule: str
@@ -101,3 +124,8 @@ class BIMQtoProperties(PropertyGroup):
         qto_name: str
         prop_name: str
         fallback: bool
+        target_unit_length: str
+        target_unit_area: str
+        target_unit_volume: str
+        target_unit_mass: str
+        target_unit_time: str
diff --git a/src/bonsai/bonsai/bim/module/qto/ui.py b/src/bonsai/bonsai/bim/module/qto/ui.py
index 032df25b20..5cfcd5ba96 100644
--- a/src/bonsai/bonsai/bim/module/qto/ui.py
+++ b/src/bonsai/bonsai/bim/module/qto/ui.py
@@ -17,9 +17,12 @@
 # along with Bonsai.  If not, see <http://www.gnu.org/licenses/>.
 
 import bpy
+import ifc5d.qto
 
 import bonsai.tool as tool
+from bonsai.bim.helper import prop_with_search
 from bonsai.bim.module.qto.data import QtoData
+from bonsai.bim.module.qto.prop import MEASURE_TO_TARGET_UNIT_FIELD
 
 
 class BIM_PT_qto(bpy.types.Panel):
@@ -44,6 +47,14 @@ class BIM_PT_qto(bpy.types.Panel):
         row = layout.row()
         row.prop(props, "qto_rule", text="")
         row.prop(props, "fallback", text="", icon="RADIOBUT_ON" if props.fallback else "RADIOBUT_OFF")
+
+        box = layout.box()
+        box.label(text="Target Units (optional, otherwise project default)")
+        for field_name, _special_type, label in MEASURE_TO_TARGET_UNIT_FIELD.values():
+            row = box.row(align=True)
+            row.label(text=label)
+            prop_with_search(row, props, field_name, text="")
+
         row = layout.row()
         row.operator("bim.perform_quantity_take_off")
 
@@ -66,6 +77,15 @@ class BIM_PT_qto_manual(bpy.types.Panel):
         row = layout.row()
         row.prop(props, "calculator_function", text="Function")
 
+        calculator = ifc5d.qto.calculators.get(props.calculator)
+        function = calculator.functions.get(props.calculator_function) if calculator else None
+        target_unit_field = MEASURE_TO_TARGET_UNIT_FIELD.get(function.measure) if function else None
+        if target_unit_field:
+            field_name, _special_type, label = target_unit_field
+            row = layout.row(align=True)
+            row.label(text=f"{label} Unit")
+            prop_with_search(row, props, field_name, text="")
+
         row = layout.row(align=True)
         row.prop(props, "qto_name", text="")
         row.prop(props, "prop_name", text="")
diff --git a/src/bonsai/bonsai/bim/prop.py b/src/bonsai/bonsai/bim/prop.py
index bb06a9ecb8..e951331f15 100644
--- a/src/bonsai/bonsai/bim/prop.py
+++ b/src/bonsai/bonsai/bim/prop.py
@@ -123,32 +123,39 @@ def get_attribute_enum_values(prop: "Attribute", context: bpy.types.Context) ->
     return items
 
 
-def get_attribute_unit_enum_items(prop: "Attribute", context: bpy.types.Context) -> tool.Blender.BLENDER_ENUM_ITEMS:
-    """Items for `Attribute.unit_id_enum`: "(Project Default)" plus every candidate unit
-    matching `prop.special_type`, filtered per-instance since candidates depend on the
-    attribute's own measure type (unlike the globally-shared lists in `bonsai.bim.ui.EnumData`).
+def get_unit_enum_items_for_special_type(
+    special_type: str, ifc_file: Union[ifcopenshell.file, None]
+) -> tool.Blender.BLENDER_ENUM_ITEMS:
+    """Items for a unit-override picker: "Default (<symbol>)" plus every candidate unit
+    matching `special_type`, filtered per-caller since candidates depend on the measure type
+    in question (unlike the globally-shared lists in `bonsai.bim.ui.EnumData`).
     """
-    ifc_file = tool.Ifc.get()
-    if not ifc_file or not tool.Pset.is_measurable_special_type(prop.special_type):
+    if not ifc_file or not tool.Pset.is_measurable_special_type(special_type):
         return [(cache_string("0"), cache_string("Default"), "")]
 
-    default_symbol = tool.Pset.get_unit_symbol_for_special_type(prop.special_type, ifc_file)
+    default_symbol = tool.Pset.get_unit_symbol_for_special_type(special_type, ifc_file)
     items: list[tuple[str, str, str]] = [
         (cache_string("0"), cache_string(f"Default ({default_symbol})" if default_symbol else "Default"), "")
     ]
-    seen_ids = {0}
-    for unit in tool.Pset.get_candidate_units_for_special_type(prop.special_type, ifc_file):
+    for unit in tool.Pset.get_candidate_units_for_special_type(special_type, ifc_file):
         name = getattr(unit, "Name", None) or unit.is_a()
         symbol = ifcopenshell.util.unit.get_unit_symbol(unit)
         label = f"{name} ({symbol})" if symbol else name
         items.append((cache_string(str(unit.id())), cache_string(label), ""))
-        seen_ids.add(unit.id())
+    return items
 
-    # Defensive: real-world files sometimes carry a Unit that doesn't cleanly match our
-    # candidate-matching logic (e.g. a mismatched UnitType). Always keep the attribute's own
-    # current override selectable/representable, however unusual, so setting unit_id_enum to
-    # match an already-seeded unit_id can never raise "enum not found".
-    if prop.unit_id and prop.unit_id not in seen_ids:
+
+def get_attribute_unit_enum_items(prop: "Attribute", context: bpy.types.Context) -> tool.Blender.BLENDER_ENUM_ITEMS:
+    """Items for `Attribute.unit_id_enum`. Wraps `get_unit_enum_items_for_special_type` with a
+    defensive addition: real-world files sometimes carry a Unit that doesn't cleanly match our
+    candidate-matching logic (e.g. a mismatched UnitType). Always keep the attribute's own
+    current override selectable/representable, however unusual, so setting unit_id_enum to
+    match an already-seeded unit_id can never raise "enum not found".
+    """
+    ifc_file = tool.Ifc.get()
+    items = get_unit_enum_items_for_special_type(prop.special_type, ifc_file)
+
+    if prop.unit_id and prop.unit_id not in {int(i[0]) for i in items}:
         own_unit = ifc_file.by_id(prop.unit_id)
         name = getattr(own_unit, "Name", None) or own_unit.is_a()
         symbol = ifcopenshell.util.unit.get_unit_symbol(own_unit)
@@ -302,6 +309,20 @@ def get_display_name(self: "Attribute") -> str:
     return f"{name}, {self.unit_symbol}"
 
 
+def get_unit_symbol(self: "Attribute") -> str:
+    """The symbol for whatever unit the value is currently expressed in: this property's own
+    override (`unit_id`) if set, else the project default for `special_type`. Computed fresh on
+    every access (rather than cached at import time) so it stays correct immediately after the
+    unit picker changes `unit_id`, and after the project's own default units are edited.
+    """
+    if not tool.Pset.is_measurable_special_type(self.special_type):
+        return ""
+    if not (ifc_file := tool.Ifc.get()):
+        return ""
+    unit = tool.Pset.resolve_effective_unit(self.special_type, self.unit_id, ifc_file)
+    return ifcopenshell.util.unit.get_unit_symbol(unit) if unit else ""
+
+
 AttributeDataType = Literal["string", "integer", "float", "boolean", "enum", "file", "list[string]"]
 # Either "", "DATE", "DATETIME", "LOGICAL", "URI", "DURATION", or an
 # IfcUnitEnum/IfcDerivedUnitEnum value with the "UNIT" suffix stripped (e.g.
@@ -359,7 +380,7 @@ class Attribute(PropertyGroup):
     value_max: FloatProperty(description="This is used to validate int_value and float_value")
     value_max_constraint: BoolProperty(default=False, description="True if the numerical value has an upper bound")
     special_type: StringProperty(name="Special Value Type", default="")
-    unit_symbol: StringProperty(name="Unit Symbol", default="")
+    unit_symbol: StringProperty(name="Unit Symbol", get=get_unit_symbol)
     unit_id: IntProperty(name="Unit Override", default=0)
     """STEP id of this property/quantity's own Unit override. 0 means "use the project default"."""
     unit_id_enum: EnumProperty(items=get_attribute_unit_enum_items, name="Unit", update=update_attribute_unit_id)
diff --git a/src/bonsai/bonsai/tool/pset.py b/src/bonsai/bonsai/tool/pset.py
index 9e8ac173c4..858969f455 100644
--- a/src/bonsai/bonsai/tool/pset.py
+++ b/src/bonsai/bonsai/tool/pset.py
@@ -386,12 +386,12 @@ class Pset(bonsai.core.tool.Pset):
                 metadata.is_null = value is None
                 metadata.is_optional = True
                 metadata.special_type = cls.get_special_type_for_prop(prop)
-                metadata.unit_symbol = cls.get_unit_symbol_for_prop(prop, tool.Ifc.get())
-                # The prop's OWN Unit override only, not the resolved project-default fallback
-                # get_unit_symbol_for_prop() above already accounted for. Some real-world files
-                # (e.g. certain exporters) set Unit on properties that aren't actually measures --
-                # ignore it there, since we only ever treat Unit as meaningful for measurable
-                # special_types (matching the UI picker's own gating).
+                # The prop's OWN Unit override only -- metadata.unit_symbol is computed fresh from
+                # special_type/unit_id on every access (see Attribute.get_unit_symbol), so it
+                # already accounts for the project-default fallback once unit_id is set below.
+                # Some real-world files (e.g. certain exporters) set Unit on properties that
+                # aren't actually measures -- ignore it there, since we only ever treat Unit as
+                # meaningful for measurable special_types (matching the UI picker's own gating).
                 own_unit = getattr(prop, "Unit", None) if cls.is_measurable_special_type(metadata.special_type) else None
                 metadata.unit_id = own_unit.id() if own_unit else 0
                 metadata.unit_id_enum = str(metadata.unit_id)
@@ -472,7 +472,6 @@ class Pset(bonsai.core.tool.Pset):
         metadata.is_optional = True
         metadata.data_type = cls.get_prop_template_primitive_type(prop_template)
         metadata.special_type = cls.get_special_type_for_prop(prop_template)
-        metadata.unit_symbol = cls.get_unit_symbol_for_special_type(metadata.special_type, tool.Ifc.get())
 
         if metadata.data_type == "string":
             metadata.string_value = "" if metadata.is_null else str(data[prop_template.Name])
@@ -585,7 +584,6 @@ class Pset(bonsai.core.tool.Pset):
         metadata.is_null = value is None
         metadata.is_optional = True
         metadata.special_type = special_type
-        metadata.unit_symbol = cls.get_unit_symbol_for_special_type(special_type, tool.Ifc.get())
         metadata.set_value(metadata.get_value_default() if metadata.is_null else value)
 
     @classmethod
diff --git a/src/bonsai/bonsai/tool/qto.py b/src/bonsai/bonsai/tool/qto.py
index ec14df6f4c..90dbce4ed4 100644
--- a/src/bonsai/bonsai/tool/qto.py
+++ b/src/bonsai/bonsai/tool/qto.py
@@ -176,6 +176,19 @@ class Qto(bonsai.core.tool.Qto):
         is_ifc4x3 = ifc_file.schema == "IFC4X3"
         return {rule_id: rule for rule_id, rule in ifc5d.qto.rules.items() if rule_id.startswith("IFC4X3") == is_ifc4x3}
 
+    @classmethod
+    def get_target_units(cls) -> dict[str, ifcopenshell.entity_instance]:
+        from bonsai.bim.module.qto.prop import MEASURE_TO_TARGET_UNIT_FIELD
+
+        props = cls.get_qto_props()
+        ifc_file = tool.Ifc.get()
+        target_units: dict[str, ifcopenshell.entity_instance] = {}
+        for measure_class, (field_name, _special_type, _label) in MEASURE_TO_TARGET_UNIT_FIELD.items():
+            unit_id = int(tool.Blender.get_enum_safe(props, field_name) or "0")
+            if unit_id:
+                target_units[measure_class] = ifc_file.by_id(unit_id)
+        return target_units
+
     @classmethod
     def get_not_quantified_elements_message(cls, not_quantified_elements: set[ifcopenshell.entity_instance]) -> str:
         not_quantified_message = ""
diff --git a/src/bonsai/test/bim/test_prop.py b/src/bonsai/test/bim/test_prop.py
index 31760f3400..be377d551b 100644
--- a/src/bonsai/test/bim/test_prop.py
+++ b/src/bonsai/test/bim/test_prop.py
@@ -131,6 +131,71 @@ class TestGetAttributeUnitEnumItems(NewFile):
         assert [i[0] for i in items] == ["0"]
 
 
+class TestGetUnitEnumItemsForSpecialType(NewFile):
+    def test_matches_the_attribute_wrapper_output(self):
+        # Regression test for extracting get_unit_enum_items_for_special_type out of
+        # get_attribute_unit_enum_items: the wrapper must still produce identical items for
+        # the plain (no own-unit-fallback-needed) case.
+        ifc = ifcopenshell.file()
+        tool.Ifc.set(ifc)
+        ifcopenshell.api.root.create_entity(ifc, ifc_class="IfcProject")
+        length_mm = ifcopenshell.api.unit.add_si_unit(ifc, unit_type="LENGTHUNIT", prefix="MILLI")
+        ifcopenshell.api.unit.assign_unit(ifc, units=[length_mm])
+        ifcopenshell.api.unit.add_si_unit(ifc, unit_type="LENGTHUNIT")
+
+        element = ifc.createIfcWall()
+        prop = ifc.createIfcPropertySingleValue(Name="Foo", NominalValue=ifc.createIfcLengthMeasure(2.5))
+        metadata = import_single_property(ifc, element, prop)
+
+        direct_items = bonsai.bim.prop.get_unit_enum_items_for_special_type(metadata.special_type, ifc)
+        wrapper_items = bonsai.bim.prop.get_attribute_unit_enum_items(metadata, bpy.context)
+        assert direct_items == wrapper_items
+
+    def test_returns_just_default_when_ifc_file_is_none(self):
+        assert bonsai.bim.prop.get_unit_enum_items_for_special_type("LENGTH", None) == [("0", "Default", "")]
+
+
+class TestUnitSymbolWithAreaVolumeDerivedFromLength(NewFile):
+    """Regression test: AREAUNIT/VOLUMEUNIT have no IfcDerivedUnitEnum member, so a project
+    whose area/volume default is an IfcDerivedUnit rather than a literal-UnitType-matching
+    IfcSIUnit/IfcConversionBasedUnit has no literal UnitType to match on.
+    ifcopenshell.util.unit.get_project_unit() used to only match by literal UnitType, so the
+    read-only unit symbol and the edit-mode "Default (<symbol>)" picker entry both silently
+    fell back to no symbol at all in that case.
+    """
+
+    def setup_project_with_derived_area_and_volume(self, ifc):
+        ifcopenshell.api.root.create_entity(ifc, ifc_class="IfcProject")
+        length = ifcopenshell.api.unit.add_si_unit(ifc, unit_type="LENGTHUNIT")
+        area = ifcopenshell.api.unit.add_derived_unit(ifc, "USERDEFINED", "area-ish", {length: 2})
+        volume = ifcopenshell.api.unit.add_derived_unit(ifc, "USERDEFINED", "volume-ish", {length: 3})
+        ifcopenshell.api.unit.assign_unit(ifc, units=[length, area, volume])
+
+    def test_default_picker_entry_shows_the_resolved_symbol(self):
+        ifc = ifcopenshell.file()
+        tool.Ifc.set(ifc)
+        self.setup_project_with_derived_area_and_volume(ifc)
+
+        element = ifc.createIfcWall()
+        prop = ifc.createIfcPropertySingleValue(Name="Foo", NominalValue=ifc.createIfcAreaMeasure(5.0))
+        metadata = import_single_property(ifc, element, prop)
+
+        items = bonsai.bim.prop.get_attribute_unit_enum_items(metadata, bpy.context)
+        assert items[0][1] == "Default (m2)"
+
+    def test_read_only_display_resolves_the_symbol(self):
+        ifc = ifcopenshell.file()
+        tool.Ifc.set(ifc)
+        self.setup_project_with_derived_area_and_volume(ifc)
+
+        element = ifc.createIfcWall()
+        prop = ifc.createIfcPropertySingleValue(Name="Foo", NominalValue=ifc.createIfcVolumeMeasure(5.0))
+        metadata = import_single_property(ifc, element, prop)
+
+        assert metadata.unit_symbol == "m3"
+        assert metadata.display_name == "Foo, m3"
+
+
 class TestUpdateAttributeUnitId(NewFile):
     def test_syncs_unit_id_and_converts_float_value_when_unit_id_enum_changes(self):
         ifc = ifcopenshell.file()
@@ -145,11 +210,42 @@ class TestUpdateAttributeUnitId(NewFile):
         metadata = import_single_property(ifc, element, prop)
         assert metadata.unit_id == 0
         assert metadata.float_value == 2500.0
+        assert metadata.unit_symbol == "mm"
+        assert metadata.display_name == "Foo, mm"
 
         metadata.unit_id_enum = str(length_m.id())
 
         assert metadata.unit_id == length_m.id()
         assert metadata.float_value == pytest.approx(2.5)  # converted, not just relabeled
+        # Regression test: unit_symbol/display_name used to be a snapshot taken once at import
+        # time, so picking a different unit converted the value but left the label showing the
+        # old unit's symbol.
+        assert metadata.unit_symbol == "m"
+        assert metadata.display_name == "Foo, m"
+
+
+class TestUnitSymbolReflectsLiveProjectState(NewFile):
+    def test_symbol_updates_after_a_project_default_unit_is_assigned_later(self):
+        # Regression test: unit_symbol used to be a snapshot computed once at import time, so a
+        # property/quantity imported before its measure type had a project default unit assigned
+        # kept showing no symbol even after one was added, unless the panel was closed and
+        # reopened (re-triggering import). It's now computed fresh on every access.
+        ifc = ifcopenshell.file()
+        tool.Ifc.set(ifc)
+        ifcopenshell.api.root.create_entity(ifc, ifc_class="IfcProject")
+        # No AREAUNIT assigned yet.
+
+        element = ifc.createIfcWall()
+        prop = ifc.createIfcPropertySingleValue(Name="Foo", NominalValue=ifc.createIfcAreaMeasure(5.0))
+        metadata = import_single_property(ifc, element, prop)
+        assert metadata.unit_symbol == ""
+        assert metadata.display_name == "Foo"
+
+        area = ifcopenshell.api.unit.add_si_unit(ifc, unit_type="AREAUNIT")
+        ifcopenshell.api.unit.assign_unit(ifc, units=[area])
+
+        assert metadata.unit_symbol == "m2"
+        assert metadata.display_name == "Foo, m2"
 
 
 class TestImportPsetFromExistingWithAGenericNumericValueAndAnExplicitUnit(NewFile):
diff --git a/src/bonsai/test/tool/test_qto.py b/src/bonsai/test/tool/test_qto.py
index 9ec7dc4efd..497fc064f4 100644
--- a/src/bonsai/test/tool/test_qto.py
+++ b/src/bonsai/test/tool/test_qto.py
@@ -181,6 +181,42 @@ class TestGetCalculatedObjectQuantities(test.bim.bootstrap.NewFile):
         assert quantities["NetVolume"] == 282.517
 
 
+class TestGetTargetUnits(test.bim.bootstrap.NewFile):
+    def setup_file(self):
+        ifc = ifcopenshell.file()
+        tool.Ifc.set(ifc)
+        ifcopenshell.api.root.create_entity(ifc, ifc_class="IfcProject", name="Test")
+        return ifc
+
+    def test_default_scene_state_returns_nothing(self):
+        self.setup_file()
+        assert subject.get_target_units() == {}
+
+    def test_setting_a_field_maps_it_to_its_measure_class(self):
+        ifc = self.setup_file()
+        metre = ifc.createIfcSIUnit(None, "LENGTHUNIT", None, "METRE")
+        millimetre = ifc.createIfcSIUnit(None, "LENGTHUNIT", "MILLI", "METRE")
+        ifcopenshell.api.unit.assign_unit(ifc, units=[metre])
+
+        props = tool.Qto.get_qto_props()
+        props.target_unit_length = str(millimetre.id())
+
+        assert subject.get_target_units() == {"IfcLengthMeasure": millimetre}
+
+    def test_untouched_fields_are_excluded(self):
+        ifc = self.setup_file()
+        metre = ifc.createIfcSIUnit(None, "LENGTHUNIT", None, "METRE")
+        millimetre = ifc.createIfcSIUnit(None, "LENGTHUNIT", "MILLI", "METRE")
+        gram = ifc.createIfcSIUnit(None, "MASSUNIT", None, "GRAM")
+        ifcopenshell.api.unit.assign_unit(ifc, units=[metre, gram])
+
+        props = tool.Qto.get_qto_props()
+        props.target_unit_length = str(millimetre.id())
+        props.target_unit_mass = "0"  # explicitly left at "Default"
+
+        assert subject.get_target_units() == {"IfcLengthMeasure": millimetre}
+
+
 class TestGetBaseQto(test.bim.bootstrap.NewFile):
     def test_run(self):
         ifc = ifcopenshell.file()