About OnlineProtractors
OnlineProtractors.com is a small, independent site with one goal: to be the fastest, most accurate and easiest-to-use place to measure an angle, on any device, for free.
Who it's for
- Students and parents checking geometry homework or learning to use a protractor.
- Teachers who need a big, clear protractor to project in class, or printable protractors for the whole room.
- Woodworkers, carpenters and DIYers setting miter saws, checking roof pitch, stairs and ramps.
- Designers, engineers and hobbyists measuring angles in drawings, screenshots and photos.
- Coaches and athletes checking joint angles and form in photos.
How the tools work
Every tool on this site runs entirely in your web browser. The online protractor is drawn as a vector graphic, so it stays sharp at any size, and the angle is calculated from the exact positions of its arms. The angle finder reads your phone's built-in motion sensor. The photo tool and camera process images locally on your device. After your first visit the tools are stored by your browser so they work offline.
Privacy first
Nothing you measure is uploaded. Your photos, camera frames and sensor readings never leave your device, and there is no account to create. We only store small preferences (like dark mode or your screen calibration) in your own browser. Read the privacy policy for details.
Accuracy
The math behind every tool is covered by automated tests, from angle calculations to unit conversions, roof pitch and miter formulas. On-screen measurements can be calibrated to real size with a credit card. If you ever find a mistake, please let us know and we will fix it quickly.
Contact
Questions, ideas or bug reports: hello@onlineprotractors.com.