Tutorial
Scale calibration
Angles never need a scale. Lengths do.
1. Click two reference points
Open Calibration in the sidebar and click two points whose real-world distance you know — a ruler edge, a dimension line, or a standard object in the photo.
2. Enter the known length
Type the distance and pick a unit. Reference points are stored in image space, so rotating or flipping the image does not break calibration.
3. Measure lengths
The Length tool reports in your chosen unit. Calibration is accurate on one plane only — features nearer or farther from the camera are at a different scale.