Protractor app for Android

What your Android phone needs

Two sensors do the work. The accelerometer senses which way gravity pulls, which is what turns the phone's tilt into an angle in degrees — every Android phone has one. The gyroscope tracks rotation and keeps that reading steady while you move; nearly all mid-range and flagship phones include it, and a few budget models don't, in which case the number simply takes a moment longer to settle. Android exposes both through the Android sensor framework, which is what the app reads. The camera protractor needs nothing more than a rear camera.

Minimum requirement: Android 8.0 (Oreo) or newer. No permissions are requested beyond the camera, and that only when you open camera mode.

Every mode, same as on iPhone

• Angle — rest the phone on a surface and read its angle in degrees. The digital angle finder mode.
• Slope and incline — the same tilt shown as percent grade or an X-in-12 ratio, so the phone doubles as an inclinometer.
• Bubble level — a digital spirit level with a live degree readout for hanging shelves and art.
• Camera protractor — measure an angle on a live view or a saved photo, for anything you can't lay a phone against.
• Reference / zeroing — zero against one surface, then measure a second relative to it.

Android vs iPhone accuracy

The maths is identical on both platforms — the difference is hardware consistency. Apple ships a single calibrated sensor package across every iPhone, so readings are uniform out of the box. Android spans hundreds of models, so sensor quality varies: a flagship matches the iPhone within about a degree, while a very cheap handset can drift a little more. The fix on either platform is the same — let the reading settle, and zero against a surface you trust before measuring one you don't.

Android-specific tips

• Take the case off. A thick or uneven case is the single most common source of a degree or two of error, because it stops the phone lying flat.
• Let it settle. Android sensors are sampled at varying rates by model; hold still for a second before reading.
• Check for a built-in offset. Lay the phone on a surface you know is true. If it reads 0.5° instead of 0°, zero the app there and that bias disappears from every reading after it.
• Battery savers throttle sensors. Aggressive power-saving modes on some manufacturers' skins can slow the sensor stream — turn them off if the readout lags.

For the full technique, see how it works and how to measure an angle. On an iPhone instead? Everything on the home page applies — the app is the same.