Two modes: drag points on the canvas to measure an on-screen angle, or use gyro mode to capture real-world tilt angles by rotating your phone.
On-screen mode: angle between two lines from canvas centre. Gyro mode: difference in DeviceOrientation beta (pitch) between Set start and Set end snapshots. iOS requires permission tap before gyro mode works.
Drag the two black dots. Angle is measured from the centre.
Drag the two black dots anywhere on the canvas. We draw lines from a central pivot to each dot and compute the included angle in degrees. Useful for measuring angles on a photo, a printed plan, or a diagram you have on screen. For real-world objects, switch to gyro mode and rotate your phone to match the angle physically.
We snapshot the device's beta (pitch) when you tap 'Set start', track changes as you tilt, and report the difference when you tap 'Set end' — or live, in 'Live' mode. Hold the phone against the surface you're measuring; the long edge is the reference. Useful for roof pitches, ramp angles, furniture tilt — anything you can rest the phone against.
On a still phone, the accelerometer-derived tilt is ±0.5°. While moving, the gyro adds short-term accuracy but drifts over 10-30 seconds. Take readings within a few seconds of tapping 'Set start'; for long measurements, set start and end fresh. Don't trust ±0.1° precision — the readings are quantised by sensor fusion.
Use the on-screen mode, drag both dots over the angle on screen. The protractor doesn't know about photo perspective — if the photo is taken at an angle, the measured angle won't match reality. For accurate field measurements, use gyro mode against the actual object.
Spirit level measures deviation from horizontal (or vertical for plumb). Protractor measures the angle between two arbitrary directions or between two snapshots of phone orientation. If you want to know 'is this shelf level?' use /sensor/level. If you want 'what's the angle of this roof slope?' use this protractor in gyro mode.
Yes — the dots are draggable on touch, mouse, and stylus. On phones, use a finger; on a tablet, an Apple Pencil or S Pen makes precise placement easier. Pinch-to-zoom is disabled inside the canvas so dragging doesn't trigger a zoom gesture.