Tutorial

Scale calibration

Angles never need a scale. Lengths do — and only for features on the same plane as your reference.

Skip this page if you only need degrees. For the three-click angle flow, see how to use.

1. Pick a known reference on the same plane

A printed ruler, a dimension line, or an object of known size that sits in the same plane as the lengths you will measure. A coin in the foreground of a roof photo will mis-scale the roof.

2. Open Scale and start a known distance

In the sidebar, open Scale (shortcut K) and followSet a scale. The panel asks you to click the first end of that known distance on the image.

Right-angle sample labelled 90 deg corner beside the Scale panel asking to click the first end of a known distance, with Set scale and Cancel. — Scale is ready: click two ends of a known length on the drawing (for example the labelled baseline), then type that real distance. The product does not draw extra markers on those clicks — the panel tells you which end to click.

3. Click both ends, then enter the real length

Click the first endpoint, then the second. Type the real-world distance and pick a unit (mm, inches, feet, and so on). Reference points live in image space, so rotate or flip after calibration does not break the scale.

4. Measure lengths

The Length tool then reports in that unit. The ruler overlay uses the same unit once a scale is set.

5. Respect the single-plane limit

Anything nearer or farther from the camera is at a different scale. That is why this is not a 3D survey tool. For structural, safety-critical, or clinical work, confirm with a calibrated instrument — see thedisclaimer.

Common mistakes

Calibrating on a foreground object for a background length.
Expecting angles to change after a scale is set — they will not.
Using a scale from one photo on a different photo or PDF page.

Open the tool ·Disclaimer