Calculate Weight in FreeCAD with Material Density

Calculating the weight of a 3D model in FreeCAD requires defining the object's material density and evaluating its volume. This guide walks you through the straightforward process of assigning material cards with predefined densities, applying custom density values directly to parts, and obtaining accurate mass and weight readouts using FreeCAD's built-in tools.

Step 1: Assign a Material to Your Object

FreeCAD uses material definitions to assign physical properties, including density, to solid shapes.

  1. Open your model and select the solid body or part in the Tree View.
  2. Switch to the Material Workbench (or access materials via the FEM Workbench if you are on an older version).
  3. Click the Material icon (palette or material card icon) in the toolbar.
  4. In the dialog that appears, select a predefined material from the drop-down list (such as Steel, Aluminum, or ABS Plastic). The density field will automatically populate with standard values (e.g., \(7850\text{ kg/m}^3\) for steel).
  5. If you need a custom density, choose User Defined or manually overwrite the value in the Density field.
  6. Click OK to assign the material to your part.

Step 2: Calculate Mass and Weight

Once the density is assigned, you can calculate the mass using FreeCAD's measurement features or properties inspector.

Method A: Using the Measurement Tool

  1. Switch to the Part Workbench.
  2. Select your object in the tree view.
  3. Go to the top menu and select Part > Measure > Measure Mass Properties (or Inspect basic shape properties).
  4. The calculation output will display the volume, center of gravity, and total calculated mass based on the active material card.

Method B: Checking Object Properties Manually

  1. Select your body or part.
  2. Look at the Property View (Data tab) in the lower left corner.
  3. Expand the Shape property to find the Volume measured in cubic millimeters (\(\text{mm}^3\)).
  4. Multiply this volume by your material's density to verify the exact mass: \[\text{Mass (g)} = \text{Volume (cm}^3\text{)} \times \text{Density (g/cm}^3\text{)}\]

For automated weight readouts, many users install the FCInfo macro via Tools > Addon manager.

  1. Run the FCInfo macro from the Macro menu.
  2. Select your part in the viewport.
  3. The panel immediately reads the density from the applied material card, computes the total volume, and displays the object's total mass and weight in your chosen units.