Angle & slope
Rest your iPhone on any surface and the motion sensors read the exact tilt — angle, incline, or roof pitch — to a fraction of a degree.
Measure any angle,
right from your pocket.
Protractor is an iOS and Android app that measures angles, slopes, inclines, and level using the phone'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 protractor app for iPhone and Android. Measure angles, slopes, and level with your phone's motion sensors and camera — no physical protractor needed. Free to try, ad-free.
18
measuring modes
Ad-free
no distractions
Offline
works anywhere
FEATURES
Every angle, slope and level — in one app.
Camera protractor
Point the camera and drag the on-screen arms to measure an angle in a photo. No surface contact needed.
Bubble level
A built-in spirit level shows true horizontal and vertical, so you can hang and align anything dead straight.
HOW IT WORKS
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Rest your iPhone on any surface and Protractor reads the exact angle and slope in real time. No physical protractor needed.
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A live degree readout updates as you tilt the phone — measure angles, inclines and roof pitch to a fraction of a degree.
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Switch between degrees, percent slope and ratio, and zero the angle against any reference surface in one tap.
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Use the camera protractor to measure an angle in a photo, or the bubble level to check true horizontal and vertical.
TESTIMONIAL
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"I hang a lot of gallery walls, and getting every frame perfectly level used to be guesswork. Now I just rest my phone on the frame and read the angle. Everything lines up."
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"For mitre joints and bevel cuts I need the exact angle, not a rough guess. Protractor reads it off the workpiece in a second — I've stopped reaching for my bevel gauge."
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"Measured my roof pitch from the ground before ordering tiles — held the phone against the gable and had the angle in degrees instantly. Saved me climbing a ladder."
FREQUENTLY ASKED QUESTIONS
What is the Protractor app?
Protractor is an iOS and Android app that measures angles, slopes, inclines, and level using your phone'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.
How does an iPhone measure angles without a physical protractor?
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.
How accurate is the Protractor app?
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.
Can it measure slope, incline, and roof pitch too?
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.
Is there a bubble level in the app?
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.
Is the Protractor app free?
Protractor is free to try and ad-free. Core measuring works offline with no account required.
BLOG
How to Draw an Angle With a Protractor (Any Degree)
The universal four-step method for drawing any angle with a protractor — with worked examples at 45° and 120°, reflex angles, and how to check your work.
How to Measure (and Mark) a 30-Degree Angle
Four ways to measure and mark a 30-degree angle — protractor, speed square, 30-60-90 triangle, or the 2:1 hypotenuse trick — plus a phone check of the cut.
New to protractors? Start with How to use a protractor, try the online protractor, or print a printable protractor.
Measure any angle,
right from your pocket.
Protractor turns your phone into a precision angle finder, level and inclinometer. Measure anything, anywhere.
Download the App