Measure Radius & Diameter
Click three points on the edge of any circle and read radius and diameter.
or browse filesdrop an image here or paste · see all measuring tools
Line size
Click three points on the edge of any circle and read radius and diameter.
or browse filesdrop an image here or paste · see all measuring tools
Drag points to adjust - right-click deletesDrag points to adjust - delete with ×
Click any three points on the edge of a circle and the tool fits the exact circle through them: radius and diameter appear instantly, drawn on the photo with the computed center marked. No need to find the center yourself. When the center IS marked, like on technical drawings, switch to Center + edge mode and two clicks do it. Values read in pixels by default, or in real units like millimeters and inches once you calibrate with any known length in the picture. Measure several circles, keep them all visible, and copy the values together.
Any object of known size makes the photo measurable: a ruler in the shot, a scale bar on a drawing, a coin, a standard sheet of paper. Measure the known length once, type its value, and every radius and diameter after that reads in real units.
Pipe and hole diameters in workshop photos, circles on engineering drawings and CAD exports, round tables and fixtures on floor plans, wheel and gear sizes, arcs in logo and design work, plates and openings in product photos. Because only the visible edge matters, even partially hidden circles measure fine: three clicks on the visible arc are enough.
Circles are one of five measurements in the same engine: distance, angles, area and perimeter each have their own page, and the full Measure Image tool switches between all of them. For pixel positions there is the coordinate finder, and for a picture's own dimensions the image size finder. The full measuring collection shows them all side by side.
The photo never leaves your device: every click and every calculation happens in your browser. No upload, no account.
Click any three points on the circle's edge. The tool fits the exact circle through them and shows radius and diameter immediately, drawn on the photo with the center marked, in pixels or in real units once calibrated.
No, that is the point of the three edge clicks: the tool computes the center for you and marks it with a small cross. And when the center is already marked, like on a technical drawing, switch to Center + edge mode and measure with just two clicks.
Yes. Only the edge matters, so three clicks on the visible arc are enough to reconstruct the whole circle, its center, radius and diameter.
Yes. Switch to real units and measure any known length in the picture once, like a ruler or a scale bar, then type its value. Every circle after that reads in your chosen unit.
No. The image opens in your browser and every calculation happens on your device. Nothing is sent to any server.