How to Edit Constraint Values in FreeCAD Sketch

Editing an existing dimensional constraint in FreeCAD is a fundamental parametric modeling task that allows you to resize sketch geometry accurately. This guide explains how to quickly modify dimensional values—such as lengths, distances, radii, and angles—either directly within the 3D viewport or through the Sketcher constraints list in the Tasks panel.

Method 1: Double-Click the Dimension in the 3D View

  1. Enter Sketch Edit Mode: In the Tree view, double-click the sketch containing the constraint you want to modify to open the Sketcher workbench.
  2. Locate the Dimension: In the 3D viewport, hover over the numerical value of the dimensional constraint (e.g., length, radius, or angle) until it highlights.
  3. Open the Edit Dialog: Double-click the number. A small pop-up window titled Insert datum (or constraint value) will appear.
  4. Enter the New Value: Type the new dimension into the text field. You can include standard units (such as mm, in, or deg).
  5. Confirm: Click OK or press Enter. The sketch geometry will automatically update to reflect the new measurement.

Method 2: Edit via the Constraints Panel

If the dimensional text is hard to select or hidden behind other geometry in the 3D view, use the side panel:

  1. Open the sketch in edit mode.
  2. Look at the Tasks tab on the left-hand side of the screen.
  3. Expand the Constraints list.
  4. Locate the specific constraint by name or value (selecting a constraint in the list will highlight it in the 3D view).
  5. Double-click the constraint in the list to open the value input box.
  6. Enter the desired value and press Enter or click OK.

Using Formulas and Expressions

If you want the constraint driven by a formula or spreadsheet:

  • When the Insert datum dialog appears, click the small blue circle icon with an f(x) inside (or press Alt + =).
  • Enter your mathematical expression or spreadsheet cell reference, then click OK.

Once your modifications are complete, click Close at the top of the Tasks panel to exit the Sketcher and apply the changes to your 3D model.