All UOM properties are returned as double values in SI units. There is an annotation for each UOM property that defines its Unit Category. The example below shows the DryWeightSiValue property on the ShipStructurePart Entity type has a Unit Category of Mass:
<Annotations Target="Com.Ingr.Smart3d.V1.ShipStructurePart/DryWeightSiValue">
<Annotation Term="Com.Ingr.Core.V1.DisplayName"
String="Dry Weight"/>
<Annotation Term="Org.OData.Core.V1.Description"
String="IJWeightCG.DryWeight"/>
<Annotation Term="Com.Ingr.Measures.V1.UnitCategory"
String="Mass"/>
</Annotations>
You are required to do any needed formatting.