The Onshape Mass properties tool is available in Part Studio and Assemblies for parts and assemblies. Find the Mass properties tool in the bottom right corner of the interface (desktop, shown below in a screenshot) or on the main toolbar (iOS and Android), the scales icon, when you have parts selected.

You can also use this tool to override properties and supply your own values for mass.

Example of location of Mass Properties tool

Properties are additive: for each additional part you select, its properties are added to the calculations in the dialog (desktop) or panel (iOS and Android). When you apply materials to parts, the density of the material is used in the calculations in the Mass properties dialog/panel. If a part has no material assigned, no figure for that part is used in the calculation (and a note is displayed in the dialog/panel to that effect).

Results of mass property calculations are approximate. The calculation of the properties may vary in accuracy, depending on the complexity of the geometry.

Enabling Show calculation variance displays the value and the difference between the lower and upper bound of the calculated value. If Show calculation variance is not enabled, the computed value without the bounds is displayed. The computations of the values are not affected by the state of the Show calculation variance checkbox.

Apply Materials to parts through the context menu on a part in the Parts list (or the graphics area).

The Mass properties tool allows you to view and override Mass, Volume, Surface area, Center of Mass, and Inertia for Parts in Part Studios and Assemblies. First, Parts must have a material assigned to them. Right-click the Part and select Edit Material. Then assign a pre-made material from the Library or select Custom and enter values. The density of the material is used in the Mass properties calculations. Next, click the Mass properties tool at the bottom right corner. Select the parts to include in the calculations. If a part has no material assigned, it is not used in the calculations and displays red (for example, the Spindle here). Properties are additive: each additional part selected adds to the calculations in the dialog. Click the red x to exit the Mass properties dialog.

Mass properties is also available from Assemblies. Click the Mass properties tool and then select the parts to make up the calculations. Click the red x to exit the dialog.

  1. To access the Mass Properties dialog, click the small scale icon Mass properties tool icon in the bottom right corner of the interface.

    Making selections in the graphics area and showing the Mass properties dialog

  2. Click the dropdown and select either Part to get the mass properties for an entire part(s) or Face to get the mass properties for a cross section or face(s).
  3. Make your selections in the graphics area.

    4. The center of mass is marked with on the model when the Mass properties dialog is open, as shown in the image above and in the image below.

  4. If you wish to override calculations and enter your own values for Mass, select the entire assembly in the Instances list on the left. Then place a check in the Mass Override box and enter the desired value. Appropriate recalculations are made once a new value is entered.

    Example of overriding calculations for mass

For any intersecting parts, the properties are calculated for each individual whole part and added together.

You are able to use the information displayed to enter values elsewhere in the system, for example, as a dimension.

  1. With the Mass properties dialog expanded, click the value to view and highlight the max precision, click again to toggle the view to value with default decimal place setting; use shortcut keys to copy to clipboard.
  2. The Mass Properties dialog provides the following information, presented from top down as shown in the tool:
    • A list of selected parts - Hover over a part in the list and a small red x appears beside it. Use this x to remove the part and it’s properties from the dialog and calculations. Alternately, you can click the selected part in the Parts lists to deselect it.
    • Select a Mate connector, inferred or existing (optional), to calculate the Moments of Inertia more accurately (instead of to the common centroid of the selected parts):

    Example of using Values, selecting a Mate connector in the Mass properties dialog

    • Mass of all parts that have a material applied
    • Volume of all selected parts
    • Surface area of all selected parts
    • Center of mass of all parts that have a material applied
    • Moments of inertia - With respect to the common centroid of the selected parts (not the Part Studio origin) and reported using the densities of the materials assigned to the selected parts. Any selected parts without materials assigned are omitted from the calculation. If no materials are assigned to any selected parts, no calculation is made.

Mass Properties tool icon circled in orange

Mass Properties tool icon circled in orange

If you want to override calculations and enter your own values for Mass, select the entire assembly in the Instances list on the left. Then place a check in the Mass Override box and enter the desired value. Appropriate recalculations are made once a new value is entered:

Switching to enable Override in the Mass properties dialog

  • To use the Mass properties tool; either select the tool and then select the part(s) OR select the part(s) first and then the tool.
  • You can select multiple parts at a time.
  • Parts may be selected in both the graphics area and the Feature list.

The Mass Properties dialog provides the following information, presented from top down as shown in the dialog.

The information is presented in the default units that you have set for your document. The image above is displaying mass property information in terms of inches (the default unit for this document).
To change the default units for your document, tap the Document menu icon the upper left, select Units, and select desired length, angle, and mass units.

  • Selected entities field - tap to view the list of selected entities. Swipe left on an entity in the list to reveal a delete option.
    Deleting an entity from the list will remove it from the dialog and calculations.
  • Mass of all selected entities.
  • Volume of all selected entities.
  • Surface area of all selected entities.
  • Center of mass.
  • Moments of inertia - with respect to the common centroid of the selected parts (not the Assembly origin) and reported assuming density of 1 in current document unit (mass per unit volume, for example: 1 lb/in 3).
  • If you select more than one part at a time, the combined properties of the parts are calculated.

If you want to override calculations and enter your own values for Mass, select the entire assembly in the Instances list on the left. Then place a check in the Mass Override box and enter the desired value. Appropriate recalculations are made once a new value is entered:

Example of Mass Properties tool icon circled in red

Mass Properties tool shown in Part Studios toolbar on Android application.

Example of Mass Properties tool icon circled in red

Mass Properties tool shown in Assemblies toolbar on Android application.

  • To use the Mass properties tool; either select the tool and then select the part(s) OR select the part(s) first and then the tool.
  • You can select multiple parts at a time.
  • Parts may be selected in both the graphics area and the Feature list.

Example of Mass Properties tool in use in an Assembly

The Mass Properties dialog provides the following information, presented from top down as shown in the dialog.

The information is presented in the default units that you have set for your document. The image above is displaying mass property information in terms of inches (the default unit for this document).
To change the default units for your document, tap the Document menu icon the upper left, select Units, and select desired length, angle, and mass units.

  • Selected entities field - tap to view the list of selected entities. Tap on Remove (X) to delete an entity. Deleting an entity from the list will remove it from the dialog and calculations.
  • Mass of all selected entities.
  • Volume of all selected entities.
  • Surface area of all selected entities.
  • Center of mass.
  • Moments of inertia - with respect to the common centroid of the selected parts (not the Assembly origin) and reported assuming density of 1 in current document unit (mass per unit volume, for example: 1 lb/in 3).
  • If you select more than one part at a time, the combined properties of the parts are calculated.