This online protractor measures the angle between two lines. Drag the orange handle to the corner, drag each blue handle along an edge, and the angle appears in degrees, with the long-way-round angle and radians beside it. You can load a photo from your device and measure on it, and the photo never leaves your browser.
| Output | Degrees to one decimal, the reflex angle and radians |
|---|---|
| Range | 0 to 180 degrees between the lines, plus the 360-degree complement |
| Photo mode | Load an image from your device; it stays in your browser |
| Cost | Free, no sign-up |
By Ship AI Lab. Last updated .
How the angle is worked out
The tool takes the corner point and the two end points and finds the direction of each line from the corner. The angle is the difference between the two directions, and it is always reported as the smaller of the two angles the lines make, with the larger one shown as the long way round.
Because you place the handles by eye or finger, the reading is as good as your placement. Zoom in on a photo before you load it if you need the corner to be exact, and place the corner handle on the exact meeting point of the edges.
Measuring on a photo
Photograph the object straight on, from directly in front and with the camera parallel to the surface. If you shoot from an angle, perspective changes the shapes and the angles you measure will be wrong. Load the picture, move the corner handle to the corner, then drag each blue handle along an edge.
This is useful for rafters, tile cuts, picture frames, furniture legs and roof pitch references in a photo. For a real object in front of you, the angle can be read directly with the phone’s sensors in the app.
How to measure an angle online
- Place the cornerDrag the orange handle to the point where the two edges meet.
- Set the two linesDrag each blue handle along an edge. The angle updates as you move.
- Optional: use a photoChoose a photo of the object, taken straight on, and measure on the picture.
What this protractor cannot do
- Angles in a photo are only right if the photo was taken square to the object, because perspective distorts angles.
- It measures what you place, so the result is only as precise as your handle placement.
- It cannot read the angle of a real surface. For that, the app’s protractor reads the phone’s tilt sensors.
- For cutting or construction that must be exact, check with a physical angle gauge.
Online Protractor questions, answered
How do I measure an angle online?
Drag the orange handle to the corner and each blue handle along an edge. The angle between the two lines shows in degrees at the top.
Can I measure an angle from a photo?
Yes. Choose a photo from your device and measure on it. Take the photo straight on, because photos taken from an angle distort the angles.
Is the photo uploaded anywhere?
No. The image is shown in your browser only and is never sent to a server.
What is the reflex angle?
It is the angle the long way round, which is 360 degrees minus the angle between the lines. It is shown next to the main reading.
How accurate is it?
It is as accurate as you place the handles. Zoom into your photo before loading it for a more exact corner, and use a physical gauge if the result must be exact.