Tools to measure an angle

The common tools to measure an angle are a protractor (for paper and flat work), an angle finder or sliding bevel (for corners and transfers), an inclinometer (for slope and level), and a phone app that reads the iPhone’s tilt sensors. The right one depends on whether you’re measuring on paper, on a surface, or from level.

An angle measuring tool reads the angle between two surfaces or lines and reports it in degrees. It ranges from a printed protractor you read by eye to a digital angle meter or an app that reads a tilt sensor and displays the angle as a number.

Yes. The Protractor app uses your iPhone’s built-in accelerometer and gyroscope to measure the angle of any surface you rest the phone on, and a camera mode measures angles you can’t lay the phone against. It reads in degrees, percent slope, or an X-in-12 ratio, and works offline.

Rest your phone flat on the surface and read the tilt the app reports, use the camera mode to align on-screen arms with the angle, or fall back to trigonometry by measuring the two sides and calculating. The phone method is fastest for real-world angles — see our full guide on how to measure an angle.

An angle meter (or angle measurer) is a digital tool that displays the measured angle as a number rather than a printed scale. A phone running an angle meter app does the same job using the sensors already inside it, with no extra hardware to buy or charge.

On most iPhones, a sensor-based measurement is accurate to within about a degree once the phone sits flat and still against the surface. Re-zeroing against a known flat reference before you measure improves it further. For certified or machine-shop work, use a calibrated instrument.