Photo measurement
Measure angles in an image
Drop a photo here
Or paste one with Ctrl+V. Nothing is uploaded — the image is processed on your device.
About this tool
Drop, paste or upload a photo and measure any angle in it. Magnifier for precise placement, perspective correction for off-angle shots, unlimited measurements, and export to PNG, CSV or JSON.
How photo measurement works
Step by step
- Add a photo: drop it on the page, paste it, choose a file or take one with your camera.
- Choose the kind of measurement: an angle at a corner, or Angle between lines for two lines that do not meet.
- Tap the corner first, then one point along each side. For two lines, tap two points on each. A magnifier follows your finger so the point is never hidden under it.
- Read the angle, add as many measurements as you need, and export them as an annotated PNG, a CSV for a spreadsheet, or a JSON workspace you can open again later.
Why photos distort angles, and how correction works
A camera shows a flat surface at a slant as a squashed shape, so a square corner photographed from one side no longer looks like 90°. Correct perspective fixes that for one flat plane: tap the four corners of something in that plane that you know is a rectangle, such as a door, a window or a sheet of paper, and the tool works out how the camera tilted and measures as if you had shot the plane straight on.
The correction only applies to angles lying in the same plane as the rectangle. Lines on a different wall, or on something standing out from it, still carry their own distortion.
Getting an accurate reading
- Photograph the angle as square-on as you can, and let it fill the frame.
- Keep it away from the edges of wide-angle or phone ultra-wide shots, where lens distortion bends straight lines. Perspective correction does not remove lens distortion.
- Spread the points along each line as far apart as the line allows: the margin of error shrinks as they move apart.
- For a slope you can reach, the inclinometer reads it directly and avoids the photo altogether.
Frequently asked questions
How do you measure an angle in a photo?
Add the photo on this page by dropping, pasting or choosing it, then tap three points: the corner first, then a point along each side. The angle appears straight away, and a magnifier helps you place each point exactly. For two lines that do not meet, choose Angle between lines and tap two points on each line.
A photo taken from off to one side distorts the angles in it. Turn on perspective correction and tap the four corners of something you know is rectangular, such as a door or a sheet of paper, and the angle is measured as if you had shot it straight on. The photo is processed on your device and never uploaded.
How accurate is measuring an angle from a photo?
The calculation is exact; the uncertainty comes from the photo and from where the points are placed. The page shows a margin of error for each measurement, and it shrinks as you spread the points further apart along each line.
The two things a reading cannot fix by itself are shooting at a slant, which perspective correction handles for one flat plane, and lens distortion near the edges of wide-angle shots, which it does not. For safety-critical work, check the result with a physical instrument.
What kind of photo works best for measuring angles?
A sharp photo taken straight on to the surface, with the angle near the middle of the frame and filling as much of it as possible. Phone main cameras distort less than ultra-wide ones, and a photo at full resolution gives more pixels to place each point on.
Screenshots and scanned drawings work well too, because they have no perspective at all. For an angle on your screen, the on-screen protractor lets you paste a screenshot and measure it directly.
Guides
About these measurements
Readings are estimates taken from rendered pixels and consumer device sensors. Do not rely on them for structural engineering, surveying, manufacturing inspection, navigation, or medical decisions. Check anything safety-critical with a calibrated instrument.
All processing happens in your browser. No image, camera frame or sensor reading is ever uploaded.
Other ways to measure
Protractor
Drag to measure, on screen
A precise on-screen protractor. Drag a vertex and two arms for an exact reading, or use the classic rotating protractor face with both scales. Paste a screenshot to measure anything on your screen.
Camera measurement
Sight an angle through your camera
Aim your camera at a roofline, a tree or a slope and read the angle of elevation. Add the distance to work out the height, and hold the reading to note it down.
Inclinometer
Turn your phone into a level
A digital level, inclinometer and plumb gauge using your phone's tilt sensor. Two-position calibration, auto-hold when steady, and readings in degrees, percent grade, roof pitch or rise-and-run.