# Protractor — Angle, Slope & Level Measure

> 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. Free to try, ad-free, works offline.

## App
- Name: Protractor — Angle, Slope & Level Measure
- Platform: iOS (iPhone 8+) and Android (8.0+)
- Price: Free to download with a free trial; a subscription unlocks the full feature set after the trial. No ads.
- Publisher: Appcellent
- App Store: https://apps.apple.com/us/app/id6742701087
- Google Play: https://play.google.com/store/apps/details?id=co.appcellent.protractor
- Category: Utilities

## How it works
The phone's built-in accelerometer and gyroscope sense gravity and orientation. Protractor reads those sensors to calculate the exact tilt of the phone, so resting it on a surface returns that surface's angle in degrees. The same reading can be shown as percent slope or a ratio, turning the app into an inclinometer for ramps, driveways, and roof pitch. A camera mode measures angles directly on a photo, and a built-in spirit (bubble) level shows true horizontal and vertical.

## Key resources
- [Home](https://protractorapp.com/): Overview and download
- [How it works](https://protractorapp.com/how-it-works/): Step-by-step usage guide
- [Online protractor](https://protractorapp.com/online-protractor/): Free interactive in-browser protractor; also an image protractor — open or drop a photo and measure the angle in it (nothing is uploaded)
- [Printable protractor](https://protractorapp.com/printable-protractor/): Free real-size 180° and 360° paper protractor — print-ready PDF for US Letter and A4, plus SVG; print at 100% / Actual size and check the built-in ruler
- [How to use a protractor](https://protractorapp.com/blog/how-to-use-a-protractor/): Step-by-step guide — origin on vertex, inner vs outer scale, reading, drawing, reflex angles
- [Angle finder](https://protractorapp.com/angle-finder/): What an angle finder is, digital vs manual, and the app as a digital angle finder
- [Measure an angle](https://protractorapp.com/measure-angle/): Tools and methods to measure an angle in degrees, including whether you can use your phone as a protractor
- [Angle ruler](https://protractorapp.com/angle-ruler/): Angle rulers, bevels, and the iPhone as a digital angle ruler
- [Digital level](https://protractorapp.com/digital-level/): Bubble level / spirit level / digital level with a live degree readout
- [Inclinometer](https://protractorapp.com/inclinometer/): Inclinometer / clinometer / slope meter — measure incline in degrees, percent grade, or ratio
- [Roof pitch calculator](https://protractorapp.com/roof-pitch-calculator/): Interactive calculator — convert rise/run, degrees, percent, and X-in-12 pitch
- [FAQ](https://protractorapp.com/faq/): Common questions about accuracy, supported devices, privacy
- [Blog](https://protractorapp.com/blog/): How-to guides for measuring angles, slope, and level
- [Best protractor app](https://protractorapp.com/best-protractor-app/): How to choose an angle-measuring app
- [Protractor for Android](https://protractorapp.com/protractor-app-for-android/): Android version — sensor requirements, Android vs iPhone accuracy, tips
- [Download](https://protractorapp.com/download/): App Store and Google Play links
- [Contact](https://protractorapp.com/contact/): Support and press

## Target audience
DIY homeowners, woodworkers, carpenters, roofers, makers, students, and physical-therapy users who need to measure an angle, slope, incline, roof pitch, or level and do not have a physical protractor or inclinometer on hand.

## Key benefit
Replaces a physical protractor, spirit level, and inclinometer with one app that is always on the user's phone, ad-free, and works entirely offline.