diff --git a/src/ifcconvert/XmlSerializer.cpp b/src/ifcconvert/XmlSerializer.cpp
index 0eb92c7a2e..b7c9bf3408 100644
--- a/src/ifcconvert/XmlSerializer.cpp
+++ b/src/ifcconvert/XmlSerializer.cpp
@@ -27,6 +27,8 @@
 
 #include <algorithm>
 
+#include "../ifcparse/IfcSIPrefix.h"
+
 using boost::property_tree::ptree;
 using namespace IfcSchema;
 
@@ -78,9 +80,6 @@ boost::optional<std::string> format_attribute(const Argument* argument, IfcUtil:
 					unit_name = unit->Name();
 				}
 
-				// TODO add toLower() and toUpper() string helper functions for the project
-				std::transform(unit_name.begin(), unit_name.end(), unit_name.begin(), ::tolower);
-
 				value = unit_name;
 			}
 			break; }
@@ -252,7 +251,7 @@ void XmlSerializer::finalize() {
 	}
 	IfcProject* project = *projects->begin();
 
-	ptree root, header, decomposition, properties;
+	ptree root, header, units, decomposition, properties;
 	
 	// Write the SPF header as XML nodes.
 	foreach(const std::string& s, file->header().file_description().description()) {
@@ -285,7 +284,20 @@ void XmlSerializer::finalize() {
 		format_properties(pset->HasProperties(), node);
 	}
 
+	// Write all assigned units as XML nodes.
+	IfcEntityList::ptr unit_assignments = project->UnitsInContext()->Units();
+	for (IfcEntityList::it it = unit_assignments->begin(); it != unit_assignments->end(); ++it) {
+		if ((*it)->is(IfcSchema::Type::IfcNamedUnit)) {
+			IfcSchema::IfcNamedUnit* named_unit = (*it)->as<IfcSchema::IfcNamedUnit>();
+			ptree& node = format_entity_instance(named_unit, units);
+			node.put("<xmlattr>.SI_equivalent", IfcParse::get_SI_equivalent(named_unit));
+		} else if ((*it)->is(IfcSchema::Type::IfcMonetaryUnit)) {
+			format_entity_instance((*it)->as<IfcSchema::IfcMonetaryUnit>(), units);
+		}
+	}
+
 	root.add_child("ifc.header",        header);
+	root.add_child("ifc.units",         units);
 	root.add_child("ifc.properties",    properties);
 	root.add_child("ifc.decomposition", decomposition);
 
diff --git a/src/ifcgeom/IfcGeomFunctions.cpp b/src/ifcgeom/IfcGeomFunctions.cpp
index 95168585e5..4bcc8413c9 100644
--- a/src/ifcgeom/IfcGeomFunctions.cpp
+++ b/src/ifcgeom/IfcGeomFunctions.cpp
@@ -1293,43 +1293,36 @@ std::pair<std::string, double> IfcGeom::Kernel::initializeUnits(IfcSchema::IfcUn
 		if (!units || !units->size()) {
 			Logger::Message(Logger::LOG_ERROR, "No unit information found");
 		} else {
-			for ( IfcEntityList::it it = units->begin(); it != units->end(); ++ it ) {
+			for (IfcEntityList::it it = units->begin(); it != units->end(); ++it) {
 				std::string current_unit_name = "";
 				IfcUtil::IfcBaseClass* base = *it;
 				IfcSchema::IfcSIUnit* unit = 0;
-				double value = 1.f;
-				if ( base->is(IfcSchema::Type::IfcConversionBasedUnit) ) {
-					IfcSchema::IfcConversionBasedUnit* u = (IfcSchema::IfcConversionBasedUnit*)base;
-					current_unit_name = u->Name();
-					IfcSchema::IfcMeasureWithUnit* u2 = u->ConversionFactor();
-					IfcSchema::IfcUnit* u3 = u2->UnitComponent();
-					if ( u3->is(IfcSchema::Type::IfcSIUnit) ) {
-						unit = (IfcSchema::IfcSIUnit*) u3;
-					}
-					IfcSchema::IfcValue* v = u2->ValueComponent();
-					// Quick hack to get the numeric value from an IfcValue:
-					const double f = *v->entity->getArgument(0);
-					value *= f;
-				} else if ( base->is(IfcSchema::Type::IfcSIUnit) ) {
-					unit = (IfcSchema::IfcSIUnit*)base;
-				}
-				if ( unit ) {
-					if ( unit->hasPrefix() ) {
-						value *= IfcParse::IfcSIPrefixToValue(unit->Prefix());
-					}
-					IfcSchema::IfcUnitEnum::IfcUnitEnum type = unit->UnitType();
-					if ( type == IfcSchema::IfcUnitEnum::IfcUnit_LENGTHUNIT ) {
-						setValue(IfcGeom::Kernel::GV_LENGTH_UNIT,value);
-						if (current_unit_name.empty()) {
-							if (unit->hasPrefix()) {
-								current_unit_name = IfcSchema::IfcSIPrefix::ToString(unit->Prefix());
+				if (base->is(IfcSchema::Type::IfcNamedUnit)) {
+					IfcSchema::IfcNamedUnit* named_unit = base->as<IfcSchema::IfcNamedUnit>();
+					if (named_unit->UnitType() == IfcSchema::IfcUnitEnum::IfcUnit_LENGTHUNIT ||
+						named_unit->UnitType() == IfcSchema::IfcUnitEnum::IfcUnit_PLANEANGLEUNIT)
+					{
+						std::string current_unit_name;
+						const double current_unit_magnitude = IfcParse::get_SI_equivalent(named_unit);
+						if (current_unit_magnitude != 0.) {
+							if (named_unit->is(IfcSchema::Type::IfcConversionBasedUnit)) {
+								IfcSchema::IfcConversionBasedUnit* u = (IfcSchema::IfcConversionBasedUnit*)base;
+								current_unit_name = u->Name();
+							} else if (named_unit->is(IfcSchema::Type::IfcSIUnit)) {
+								IfcSchema::IfcSIUnit* si_unit = named_unit->as<IfcSchema::IfcSIUnit>();
+								if (si_unit->hasPrefix()) {
+									current_unit_name = IfcSchema::IfcSIPrefix::ToString(si_unit->Prefix()) + unit_name;
+								}
+								current_unit_name += IfcSchema::IfcSIUnitName::ToString(si_unit->Name());
+							}
+							if (named_unit->UnitType() == IfcSchema::IfcUnitEnum::IfcUnit_LENGTHUNIT) {
+								unit_name = current_unit_name;
+								unit_magnitude = current_unit_magnitude;
+								setValue(IfcGeom::Kernel::GV_LENGTH_UNIT, current_unit_magnitude);
+							} else {
+								setValue(IfcGeom::Kernel::GV_PLANEANGLE_UNIT, current_unit_magnitude);
 							}
-							current_unit_name += IfcSchema::IfcSIUnitName::ToString(unit->Name());
 						}
-						unit_magnitude = value;
-						unit_name = current_unit_name;
-					} else if ( type == IfcSchema::IfcUnitEnum::IfcUnit_PLANEANGLEUNIT ) {
-						setValue(IfcGeom::Kernel::GV_PLANEANGLE_UNIT, value);
 					}
 				}
 			}
diff --git a/src/ifcparse/IfcSIPrefix.cpp b/src/ifcparse/IfcSIPrefix.cpp
index e3edd16ed7..632760b5ee 100644
--- a/src/ifcparse/IfcSIPrefix.cpp
+++ b/src/ifcparse/IfcSIPrefix.cpp
@@ -36,4 +36,31 @@ double IfcParse::IfcSIPrefixToValue(IfcSchema::IfcSIPrefix::IfcSIPrefix v) {
 	else if ( v == IfcSchema::IfcSIPrefix::IfcSIPrefix_FEMTO ) return 1.e-15;
 	else if ( v == IfcSchema::IfcSIPrefix::IfcSIPrefix_ATTO  ) return 1.e-18;
 	else return 1.;
+}
+
+double IfcParse::get_SI_equivalent(IfcSchema::IfcNamedUnit* named_unit) {
+	double scale =  1.;
+	IfcSchema::IfcSIUnit* si_unit = 0;
+
+	if (named_unit->is(IfcSchema::Type::IfcConversionBasedUnit)) {
+		IfcSchema::IfcConversionBasedUnit* conv_unit = named_unit->as<IfcSchema::IfcConversionBasedUnit>();
+		IfcSchema::IfcMeasureWithUnit* factor = conv_unit->ConversionFactor();
+		IfcSchema::IfcUnit* component = factor->UnitComponent();
+		if (component->is(IfcSchema::Type::IfcSIUnit)) {
+			si_unit = component->as<IfcSchema::IfcSIUnit>();
+			IfcSchema::IfcValue* v = factor->ValueComponent();
+			scale = *v->entity->getArgument(0);
+		}		
+	} else if (named_unit->is(IfcSchema::Type::IfcSIUnit)) {
+		si_unit = named_unit->as<IfcSchema::IfcSIUnit>();
+	}
+	if (si_unit) {
+		if (si_unit->hasPrefix()) {
+			scale *= IfcSIPrefixToValue(si_unit->Prefix());
+		}
+	} else {
+		scale = 0.;
+	}
+
+	return scale;
 }
\ No newline at end of file
diff --git a/src/ifcparse/IfcSIPrefix.h b/src/ifcparse/IfcSIPrefix.h
index 1c62b31bdd..c90a602eb5 100644
--- a/src/ifcparse/IfcSIPrefix.h
+++ b/src/ifcparse/IfcSIPrefix.h
@@ -23,7 +23,9 @@
 #include "../ifcparse/IfcParse.h"
 
 namespace IfcParse {
-	double IfcSIPrefixToValue(IfcSchema::IfcSIPrefix::IfcSIPrefix v);
+	double IfcSIPrefixToValue(IfcSchema::IfcSIPrefix::IfcSIPrefix);
+
+	double get_SI_equivalent(IfcSchema::IfcNamedUnit*);
 }
 
 #endif
\ No newline at end of file