#### IfcConversionBasedUnit

Natural language names

##### Semantic definitions at the entity

Entity definition

Definition from ISO/CD 10303-41:1992: A conversion based unit is a unit that is defined based on a measure with unit.

> NOTE Corresponding STEP name: conversion_based_unit, please refer to ISO/IS 10303-41:1994 for the final definition of the formal standard.

> HISTORY New entity in IFC Release 1.5.1.

An inch is a converted unit. It is from the Imperial system, its name is "inch" and it can be related to the si unit, millimetre, through a measure with unit whose value is 25.4 millimetre. A foot is also a converted unit. It is from the Imperial system, its name is "foot" and it can be related to an si unit, millimetre, either directly or through the unit called "inch".

To identify some commonly used conversion based units the standard designations (case insensitive) for the Name attribute include the following:

Name | Description
'inch' | Length measure equal to 25.4 mm
'foot' | Length measure equal to 30.48 mm
'yard' | Length measure equal to 914 mm
'mile' | Length measure equal to 1609 m
'acre' | Area measure equal to 4046,86 square meters
'litre' | Volume measure equal to 0.001 cubic meters
'pint UK' | Volume measure equal to 0.000568 cubic meters
'pint US' | Volume measure equal to 0.000473 cubic meters
'gallon UK' | Volume measure equal to 0.004546 cubic meters
'gallon US' | Volume measure equal to 0.003785 cubic meters
'ounce' | Weight measure equal to 28.35 g
'pound' | Weight measure equal to 0.454 kg

Attribute definitions

# | Attribute | Type | Cardinality | Description | A
--- | --- | --- | --- | --- | ---
3 | Name | IfcLabel | [1:1] | The word, or group of words, by which the conversion based unit is referred to. | X
4 | ConversionFactor | IfcMeasureWithUnit | [1:1] | The physical quantity from which the converted unit is derived. | X

##### Inherited definitions from supertypes

Entity inheritance
Attribute inheritance

# | Attribute | Type | Cardinality | Description | A
--- | --- | --- | --- | --- | ---
IfcNamedUnit
1 | Dimensions | IfcDimensionalExponents | [1:1] | The dimensional exponents of the SI base units by which the named unit is defined. | X
2 | UnitType | IfcUnitEnum | [1:1] | The type of the unit. | X
IfcConversionBasedUnit
3 | Name | IfcLabel | [1:1] | The word, or group of words, by which the conversion based unit is referred to. | X
4 | ConversionFactor | IfcMeasureWithUnit | [1:1] | The physical quantity from which the converted unit is derived. | X

##### Formal representations

XSD Specification
`<xs:element name="IfcConversionBasedUnit" type="ifc:IfcConversionBasedUnit" substitutionGroup="ifc:IfcNamedUnit" nillable="true"/>
<xs:complexType name="IfcConversionBasedUnit">
<xs:complexContent>
<xs:extension base="ifc:IfcNamedUnit">
<xs:sequence>
<xs:element name="ConversionFactor" type="ifc:IfcMeasureWithUnit" nillable="true"/>
</xs:sequence>
<xs:attribute name="Name" type="ifc:IfcLabel" use="optional"/>
</xs:extension>
</xs:complexContent>
</xs:complexType>
`
EXPRESS Specification
`ENTITY IfcConversionBasedUnit
SUBTYPE OF (IfcNamedUnit);
Name : IfcLabel;
ConversionFactor : IfcMeasureWithUnit;
END_ENTITY;

EXPRESS-G diagram

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