Measure real-world lengths from a picture
A photo already contains the geometry you need — what it lacks is a scale. This tool lets you supply one: click both ends of any feature whose real length you know (the amber line), type that length in, and the tool computes how many image pixels equal one millimetre, metre or foot. From then on every pair of clicks becomes a measurement, labelled directly on the image in blue and listed below it. It works on floor plans, scanned documents, product photos, maps with a scale bar, PCB shots — anything with one known distance in frame.
How to measure distances on an image
- Drop, browse or paste an image.
- Set scale: click the two ends of a known-length feature, enter its real length and pick a unit.
- Measure: click any two points — the real distance appears on the canvas and in the list.
- Delete individual measurements, clear them all, or reset the scale to recalibrate.
Honest limits: calibration is everything
The results are only as good as the calibration. Two things bend them: perspective and lens curvature. A camera tilted relative to the subject makes distant parts of the scene smaller than near parts, so a scale set on one wall misreads the opposite one; wide-angle lenses additionally bow straight lines near the edges of the frame. Flat subjects photographed straight-on — plans, documents, boards — measure very well; angled photos of 3D rooms give rough figures at best. Keep the reference object in the same plane as what you measure, and recalibrate if you crop or rescale the source first with the Image Cropper or Image Resizer. And if you need a color rather than a distance from the same photo, the Image Color Picker reads any pixel in place.