Mass is a read-only property that describes the product of a part’s volume and density. It is returned by the BasePart/GetMass|GetMass function.

• The volume of a part is determined by its BasePart/Size|Size and its Part/Shape|Shape, which varies depending on the kind of BasePart used, such as WedgePart.
• The density of a part is determined by its BasePart/Material|Material or BasePart/CustomPhysicalProperties|CustomPhysicalProperties, if specified.

A common use of the Mass property is using it to calculate the magnitude of a gravity-counteracting force. Using a BodyForce, apply a upward force equal to the product of a part’s Mass and Workspace/Gravity. This will completely counteract the force of gravity on the part.