diff --git a/src/blenderbim/blenderbim/bim/module/pset/__init__.py b/src/blenderbim/blenderbim/bim/module/pset/__init__.py
index 2ba0a44e31..4cf97e2ba0 100644
--- a/src/blenderbim/blenderbim/bim/module/pset/__init__.py
+++ b/src/blenderbim/blenderbim/bim/module/pset/__init__.py
@@ -27,6 +27,7 @@ classes = (
     operator.EditPset,
     operator.EnablePsetEditing,
     operator.GuessQuantity,
+    operator.CalculateQuantity,
     operator.GuessAllQuantities,
     operator.RemovePset,
     operator.TogglePsetExpansion,
diff --git a/src/blenderbim/blenderbim/bim/module/pset/calc_quantity_function_mapper.py b/src/blenderbim/blenderbim/bim/module/pset/calc_quantity_function_mapper.py
new file mode 100644
index 0000000000..75aa45a498
--- /dev/null
+++ b/src/blenderbim/blenderbim/bim/module/pset/calc_quantity_function_mapper.py
@@ -0,0 +1,10 @@
+mapper = {
+    "Qto_WallBaseQuantities" : {
+        "Length" : "get_length",
+        "Width" : "get_width",
+        "Height" : "get_height",
+    },
+    "Qto_SlabBaseQuantities" : {
+        "Depth" : "get_height",
+    },
+}
diff --git a/src/blenderbim/blenderbim/bim/module/pset/operator.py b/src/blenderbim/blenderbim/bim/module/pset/operator.py
index 0692e4c4ec..f1f5e256c3 100644
--- a/src/blenderbim/blenderbim/bim/module/pset/operator.py
+++ b/src/blenderbim/blenderbim/bim/module/pset/operator.py
@@ -344,6 +344,44 @@ class AddQto(bpy.types.Operator, Operator):
         Data.load(IfcStore.get_file(), ifc_definition_id)
 
 
+class CalculateQuantity(bpy.types.Operator):
+    bl_idname = "bim.calculate_quantity"
+    bl_label = "Calculate Quantity"
+    bl_options = {"REGISTER", "UNDO"}
+    prop: bpy.props.StringProperty()
+
+    def execute(self, context):
+        self.qto_calculator = QtoCalculator()
+        obj = context.active_object
+        prop = obj.PsetProperties.properties.get(self.prop)
+        prop.metadata.float_value = self.calculate_quantity(obj, context)
+        return {"FINISHED"}
+
+    def calculate_quantity(self, obj, context):
+        quantity = self.qto_calculator.calculate_quantity(obj.PsetProperties.active_pset_name, self.prop, obj)
+        prefix, name = self.get_blender_prefix_name(context)
+        quantity = ifcopenshell.util.unit.convert(quantity, None, "METRE", prefix, name)
+        return round(quantity, 3)
+
+    def get_prefix_name(self, value):
+        if "/" in value:
+            return value.split("/")
+        return None, value
+
+    def get_blender_prefix_name(self, context):
+        unit_settings = context.scene.unit_settings
+        if unit_settings.system == "IMPERIAL":
+            if unit_settings.length_unit == "INCHES":
+                return None, "inch"
+            elif unit_settings.length_unit == "FEET":
+                return None, "foot"
+        elif unit_settings.system == "METRIC":
+            if unit_settings.length_unit == "METERS":
+                return None, "METRE"
+            return unit_settings.length_unit[0 : -len("METERS")], "METRE"
+
+
+
 class GuessQuantity(bpy.types.Operator):
     bl_idname = "bim.guess_quantity"
     bl_label = "Guess Quantity"
diff --git a/src/blenderbim/blenderbim/bim/module/pset/qto_calculator.py b/src/blenderbim/blenderbim/bim/module/pset/qto_calculator.py
index a5b67722da..99478f8036 100644
--- a/src/blenderbim/blenderbim/bim/module/pset/qto_calculator.py
+++ b/src/blenderbim/blenderbim/bim/module/pset/qto_calculator.py
@@ -25,9 +25,23 @@ from shapely.geometry import Polygon
 from shapely.ops import unary_union
 import blenderbim.tool as tool
 import ifcopenshell
+from blenderbim.bim.module.pset.calc_quantity_function_mapper import mapper
 
 
 class QtoCalculator:
+
+    def __init__(self):
+        self.mapping_dict = {}
+        for key in mapper.keys():
+            self.mapping_dict[key] = dict(mapper[key].items())
+
+        for key in self.mapping_dict.keys():
+            for item in self.mapping_dict[key].keys():
+                self.mapping_dict[key][item] = eval("self." + self.mapping_dict[key][item])
+
+    def calculate_quantity(self, qto_name, quantity_name, obj):
+        return self.mapping_dict[qto_name][quantity_name](obj)
+
     def guess_quantity(self, prop_name, alternative_prop_names, obj):
         prop_name = prop_name.lower()
         alternative_prop_names = [p.lower() for p in alternative_prop_names]
diff --git a/src/blenderbim/blenderbim/bim/module/pset/ui.py b/src/blenderbim/blenderbim/bim/module/pset/ui.py
index 70a1a173b7..b1408402dc 100644
--- a/src/blenderbim/blenderbim/bim/module/pset/ui.py
+++ b/src/blenderbim/blenderbim/bim/module/pset/ui.py
@@ -19,6 +19,7 @@
 from bpy.types import Panel
 from blenderbim.bim.ifc import IfcStore
 from blenderbim.bim.helper import prop_with_search
+from blenderbim.bim.module.pset.calc_quantity_function_mapper import mapper
 from blenderbim.bim.module.pset.data import (
     ObjectPsetsData,
     ObjectQtosData,
@@ -139,6 +140,11 @@ def draw_psetqto_ui(context, pset_id, pset, props, layout, obj_type):
 def draw_psetqto_editable_ui(box, props, prop):
     row = box.row(align=True)
     draw_property(prop, row, copy_operator="bim.copy_property_to_selection")
+    qto_name = ObjectQtosData.data['qtos'][0]['Name']
+    if qto_name in mapper.keys():
+        if prop.name in mapper[qto_name]:
+            op = row.operator("bim.calculate_quantity", icon="MOD_EDGESPLIT", text="")
+            op.prop = prop.name
     if (
         "length" in prop.name.lower()
         or "width" in prop.name.lower()