Disclaimer
Measurement disclaimer
A measurement from an image is evidence, not proof.
Last updated Updated September 2026
What this tool measures
It measures the angle between points you place on an image. That is not the same as the angle of the physical object the image depicts. The two agree only insofar as the image faithfully represents the object — which depends on camera position, lens, resolution and focus.
Use a calibrated instrument when
- The result affects structural or load-bearing work
- Anyone's safety depends on it
- It will be used in legal, insurance or regulatory documentation
- It must meet a manufacturing tolerance
- Material will be cut or committed on the basis of it
For these, treat a reading here as a first estimate that tells you where to point the real instrument.
Not a medical device
This tool is not a medical device and has not been evaluated by any regulator. Do not use it for clinical measurement, diagnosis, treatment decisions, or assessing range of motion for care purposes. That includes measurements on radiographs or other medical imaging.
Perspective is the main trap
If a photograph was not taken square-on to the surface being measured, the angles in the image are genuinely different from the angles on the object. The tool cannot detect this and will report a confident, precise, wrong number. This error does not shrink when you zoom in.
Scale calibration is single-plane
Setting a scale from a known distance is accurate for features on the same plane as your reference. Anything nearer to or further from the camera is at a different scale, and its lengths will be wrong.
Overlays are not calibration
The grid and the protractor dial are alignment aids. They are not evidence of physical accuracy, and they do not compensate for a poor source image.