How to measure an angle online
- Drag the dark middle handle onto the corner (vertex) of the angle.
- Drag the blue handle along one side and the red handle along the other.
- Read the angle above the arc. Tick Reflex angle to see the outside angle (over 180°).
Measuring an angle in a photo
Press Open photo and choose a picture from your phone or computer. The image opens in your browser only and is never uploaded. Take the photo square-on to the object, because shooting at a slant distorts angles. For a slope, line one arm up with something you know is level, or read the "from horizontal" value if the photo itself is level.
What people measure with it
- Roof pitch and stairsCheck a slope from a photo, then convert: a 6/12 roof pitch is about 26.6°.
- HomeworkCheck angles in a geometry worksheet photo.
- DIY and woodworkingFind the angle for a mitre or bevel cut.
- Sports and postureKnee, elbow or bike-fit angles from a side-on photo.
Roof pitch to degrees
| Pitch (rise/12) | Degrees |
|---|---|
| 2/12 | 9.5° |
| 3/12 | 14.0° |
| 4/12 | 18.4° |
| 5/12 | 22.6° |
| 6/12 | 26.6° |
| 7/12 | 30.3° |
| 8/12 | 33.7° |
| 9/12 | 36.9° |
| 10/12 | 39.8° |
| 12/12 | 45.0° |
Need a protractor you can hold? Print the printable protractor.
Frequently asked questions
Is the online protractor accurate?
The angle maths is exact. Accuracy depends on how precisely you place the handles, usually within half a degree, and on the photo being taken square-on.
Are my photos uploaded?
No. The photo is opened directly in your browser and never leaves your device.
Does it need calibration?
No. Angles do not depend on screen size, so the online protractor works on any screen without calibrating.
Last reviewed 2026-10-07.