diff --git a/src/ifcblenderexport/io_export_ifc/export_ifc.py b/src/ifcblenderexport/io_export_ifc/export_ifc.py
index 1d1e453303..c2e932b80f 100644
--- a/src/ifcblenderexport/io_export_ifc/export_ifc.py
+++ b/src/ifcblenderexport/io_export_ifc/export_ifc.py
@@ -4,6 +4,7 @@ import json
 import time
 from pathlib import Path
 from mathutils import Vector, Matrix
+from .helper import SIUnitHelper
 from . import ifcopenshell
 
 class ArrayModifier:
@@ -754,28 +755,6 @@ class IfcParser():
     def is_a_type(self, class_name):
         return class_name[0:3] == 'Ifc' and class_name[-4:] == 'Type'
 
-class SIUnitHelper:
-    prefixes = ["EXA", "PETA", "TERA", "GIGA", "MEGA", "KILO", "HECTO",
-        "DECA", "DECI", "CENTI", "MILLI", "MICRO", "NANO", "PICO", "FEMTO",
-        "ATTO"]
-    unit_names = ["AMPERE", "BECQUEREL", "CANDELA", "COULOMB",
-        "CUBIC_METRE", "DEGREE CELSIUS", "FARAD", "GRAM", "GRAY", "HENRY",
-        "HERTZ", "JOULE", "KELVIN", "LUMEN", "LUX", "MOLE", "NEWTON", "OHM",
-        "PASCAL", "RADIAN", "SECOND", "SIEMENS", "SIEVERT", "SQUARE METRE",
-        "METRE", "STERADIAN", "TESLA", "VOLT", "WATT", "WEBER"]
-
-    @staticmethod
-    def get_prefix(text):
-        for prefix in SIUnitHelper.prefixes:
-            if prefix in text.upper():
-                return prefix
-
-    @staticmethod
-    def get_unit_name(text):
-        for name in SIUnitHelper.unit_names:
-            if name in text.upper().replace('METER', 'METRE'):
-                return name
-
 class IfcExporter():
     def __init__(self, ifc_export_settings, ifc_schema, ifc_parser, qto_calculator):
         self.template_file = '{}template.ifc'.format(ifc_export_settings.schema_dir)
diff --git a/src/ifcblenderexport/io_export_ifc/helper.py b/src/ifcblenderexport/io_export_ifc/helper.py
new file mode 100644
index 0000000000..aa00fc0273
--- /dev/null
+++ b/src/ifcblenderexport/io_export_ifc/helper.py
@@ -0,0 +1,66 @@
+import math
+
+class SIUnitHelper:
+    prefixes = {"EXA": 1e18, "PETA": 1e15, "TERA": 1e12, "GIGA": 1e9, "MEGA":
+        1e6, "KILO": 1e3, "HECTO": 1e2, "DECA": 1e1, "DECI": 1e-1, "CENTI":
+        1e-2, "MILLI": 1e-3, "MICRO": 1e-6, "NANO": 1e-9, "PICO": 1e-12,
+        "FEMTO": 1e-15, "ATTO": 1e-18}
+    unit_names = ["AMPERE", "BECQUEREL", "CANDELA", "COULOMB",
+        "CUBIC_METRE", "DEGREE CELSIUS", "FARAD", "GRAM", "GRAY", "HENRY",
+        "HERTZ", "JOULE", "KELVIN", "LUMEN", "LUX", "MOLE", "NEWTON", "OHM",
+        "PASCAL", "RADIAN", "SECOND", "SIEMENS", "SIEVERT", "SQUARE METRE",
+        "METRE", "STERADIAN", "TESLA", "VOLT", "WATT", "WEBER"]
+    si_conversions = {
+        'inch': 0.0254,
+        'foot': 0.3048,
+        'yard': 0.914,
+        'mile': 1609,
+        'square inch': 0.0006452,
+        'square foot': 0.09290,
+        'square yard': 0.83612736,
+        'acre': 4046.86,
+        'square mile': 2588881,
+        'cubic inch': 0.00001639,
+        'cubic foot': 0.02832,
+        'cubic yard': 0.7636,
+        'litre': 0.001,
+        'fluid ounce UK': 0.0000284130625,
+        'fluid ounce US': 0.00002957353,
+        'pint UK': 0.000568,
+        'pint US': 0.000473,
+        'gallon UK': 0.004546,
+        'gallon US': 0.003785,
+        'degree': math.pi/180,
+        'ounce': 0.02835,
+        'pound': 0.454,
+        'ton UK': 1016.0469088,
+        'ton US': 907.18474,
+        'lbf': 4.4482216153,
+        'kip': 4448.2216153,
+        'psi': 6894.7572932,
+        'ksi': 6894757.2932,
+        'minute': 60,
+        'hour': 3600,
+        'day': 86400,
+        'btu': 1055.056}
+
+    @staticmethod
+    def get_prefix(text):
+        for prefix in SIUnitHelper.prefixes.keys():
+            if prefix in text.upper():
+                return prefix
+
+    @staticmethod
+    def get_prefix_multiplier(text):
+        if not text:
+            return 1
+        prefix = SIUnitHelper.get_prefix(text)
+        if prefix:
+            return SIUnitHelper.prefixes[prefix]
+        return 1
+
+    @staticmethod
+    def get_unit_name(text):
+        for name in SIUnitHelper.unit_names:
+            if name in text.upper().replace('METER', 'METRE'):
+                return name
diff --git a/src/ifcblenderexport/io_export_ifc/import_ifc.py b/src/ifcblenderexport/io_export_ifc/import_ifc.py
index 7637a7af32..df4eaecf19 100644
--- a/src/ifcblenderexport/io_export_ifc/import_ifc.py
+++ b/src/ifcblenderexport/io_export_ifc/import_ifc.py
@@ -5,6 +5,7 @@ import os
 import json
 import time
 import mathutils
+from .helper import SIUnitHelper
 
 cwd = os.path.dirname(os.path.realpath(__file__)) + os.path.sep
 
@@ -125,11 +126,14 @@ class IfcImporter():
     def calculate_unit_scale(self):
         units = self.file.by_type('IfcUnitAssignment')[0]
         for unit in units.Units:
-            if unit.is_a('IfcSIUnit') \
-                and unit.UnitType == 'LENGTHUNIT':
-                if unit.Prefix:
-                    if unit.Prefix == 'MILLI':
-                        self.unit_scale *= 0.001
+            if not hasattr(unit, 'UnitType') \
+                or unit.UnitType != 'LENGTHUNIT':
+                continue
+            while unit.is_a('IfcConversionBasedUnit'):
+                self.unit_scale *= unit.ConversionFactor.ValueComponent.wrappedValue
+                unit = unit.ConversionFactor.UnitComponent
+            if unit.is_a('IfcSIUnit'):
+                self.unit_scale *= SIUnitHelper.get_prefix_multiplier(unit.Prefix)
 
     def create_project(self):
         self.project = { 'ifc': self.file.by_type('IfcProject')[0] }