IFC 4.3.x development IfcConversionBasedUnit

Change log


additionsinversesHasExternalReference Semantic definitions at the entity

An IfcConversionBasedUnit is used to define a unit that has a conversion rate to a base unit. To identify some commonly used conversion based units, the standard designations (case insensitive) for the Name attribute are indicated in Table 1.


Name Description
'inch' Length measure equal to 25.4 mm
'foot' Length measure equal to 304.8 mm
'yard' Length measure equal to 914 mm
'mile' Length measure equal to 1609 m
'square inch' Area measure equal to 0.0006452 square meters
'square foot' Area measure equal to 0.09290 square meters
'square yard' Area measure equal to 0.83612736 square meters
'acre' Area measure equal to 4046.86 square meters
'square mile' Area measure equal to 2 588 881 square meters
'cubic inch' Volume measure equal to 0.00001639 cubic meters
'cubic foot' Volume measure equal to 0.02832 cubic meters
'cubic yard' Volume measure equal to 0.7636 cubic meters
'litre' Volume measure equal to 0.001 cubic meters
'fluid ounce UK' Volume measure equal to 0.0000284130625 cubic meters
'fluid ounce US' Volume measure equal to 0.00002957353 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
'degree' Angle measure equal to π/180 rad
'ounce' Mass measure equal to 28.35 g
'pound' Mass measure equal to 0.454 kg
'ton UK' Mass measure equal to 1016.0469088 kg, also known as long ton, gross ton, shipper's ton
'ton US' Mass measure equal to 907.18474 kg, also known as short ton, net ton
'lbf' Force measure equal to 4.4482216153 N, pound-force
'kip' Force measure equal to 4448.2216153 N, kilopound-force
'psi' Pressure measure equal to 6894.7572932 Pa, pound-force per square inch
'ksi' Pressure measure equal to 6894757.2932 Pa, kilopound-force per square inch
'minute' Time measure equal to 60 s
'hour' Time measure equal to 3600 s
'day' Time measure equal to 86400 s
'btu' Energy measure equal to 1055.056 J, British Thermal Unit

Table 1 — Standard unit names

EXAMPLE  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 IfcSIUnit, millimetre, either directly or through the unit called "inch". Note that several US customary units differ from Imperial units (nonmetric English units) of the same name.

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

NOTE  Entity adapted from conversion_based_unit defined in ISO 10303-41.

HISTORY  New entity in IFC1.5.1.

IFC2x3 CHANGE  Standard names of typical units added.

IFC4 CHANGE  Further names added: square inch, square foot, square mile, square yard, cubic inch, cubic foot, cubic yard, fluid ounce UK/US, ton UK/US, degree. Attributes

# Attribute Type Description
1 Dimensions IfcDimensionalExponents The dimensional exponents of the SI base units by which the named unit is defined.
2 UnitType IfcUnitEnum The type of the unit.
3 Name IfcLabel The word, or group of words, by which the conversion based unit is referred to.
4 ConversionFactor IfcMeasureWithUnit The physical quantity from which the converted unit is derived.
HasExternalReferenceSET [0:?] OF IfcExternalReferenceRelationship FOR RelatedResourceObjectsReference to external information, e.g. library, classification, or document information, which is associated with the conversion-based unit.

> IFC4 CHANGE New inverse attribute. Entity inheritance

dot_inheritance IfcConversionBasedUnitWithOffset IfcConversionBasedUnitWithOffset IfcConversionBasedUnit IfcConversionBasedUnit IfcConversionBasedUnitWithOffset->IfcConversionBasedUnit IfcNamedUnit IfcNamedUnit IfcConversionBasedUnit->IfcNamedUnit IfcContextDependentUnit IfcContextDependentUnit IfcContextDependentUnit->IfcNamedUnit IfcSIUnit IfcSIUnit IfcSIUnit->IfcNamedUnit Formal representations

ENTITY IfcConversionBasedUnit
 SUBTYPE OF (IfcNamedUnit);
	Name : IfcLabel;
	ConversionFactor : IfcMeasureWithUnit;
	HasExternalReference : SET [0:?] OF IfcExternalReferenceRelationship FOR RelatedResourceObjects;