The best protractor app for iPhone

Protractor is an iOS app that measures angles, slopes, inclines, and level using your iPhone's built-in motion sensors and camera, replacing a physical protractor, spirit level, and inclinometer. It's free to try, ad-free, and works offline.

The iPhone has a built-in accelerometer and gyroscope that sense gravity and orientation. Protractor reads those sensors to calculate the exact tilt of the phone — so resting it on a surface gives you that surface's angle in degrees. For angles you can't lay the phone on, the camera mode lets you measure the angle directly on a photo.

For everyday DIY, woodworking, and home tasks, the sensor-based reading is accurate to within about a degree on most iPhones once the phone is held flat against the surface. Re-zeroing against a known reference before measuring improves accuracy further.

Yes. The same angle reading can be shown as degrees, percent slope, or a ratio, so the app doubles as an inclinometer for measuring ramps, driveways, and roof pitch.

Yes. A built-in spirit (bubble) level shows true horizontal and vertical, so you can check whether shelves, frames, and appliances are straight without a separate level.

Protractor is free to try and ad-free. Core measuring works offline with no account required.