Online Protractor
This online protractor measures angles directly on your display. Drag the protractor overlay anywhere and rotate it until it matches your angle — or switch to angle mode and click a vertex plus two points on the rays to read the exact angle in degrees.
Calibration — Online Ruler
We match your resolution, pixel ratio, and browser against a database of 100+ device profiles to set the correct PPI instantly.
Enter your monitor or laptop diagonal in inches (printed on the box or in specs) and we calculate the exact PPI from your screen resolution.
Drag the slider until the card outline matches a real card placed on your screen.
How to use the online protractor
Open the tool above and turn on the Protractor. Drag its body to move it over the angle you want to check, then drag the top handle to rotate the semicircle until its baseline aligns with one ray and the scale reads your angle against the other. Double-click the protractor to remove it, and toggle the spacing grid underneath for quick visual alignment.
Angle mode: click three points, get the degrees
Press the Angle button, click the vertex first, then click one point on each of the two rays. The readout shows the measured angle in degrees to one decimal place. Press Esc or double-click to clear and measure the next angle. Because angles are ratios of pixel distances, this online protractor needs no calibration to be accurate.
What an online protractor is used for
Common uses: checking drafted angles in CAD-style drawings, verifying rotation angles in design mockups, working through geometry homework on screen, planning carpentry or DIY cuts from printed plans, and confirming chart slopes and roof pitches in diagrams. Anything you would otherwise hold a plastic protractor against the screen.
| Angle | Common name | Everyday use |
|---|---|---|
| 30° | Acute | Roof pitch, clock-hand positions |
| 45° | Acute | Diagonal layouts, miter cuts |
| 90° | Right | Corners and grid alignment |
| 180° | Straight | Baseline and straightness checks |
| 0° | Degenerate | Perfect alignment of two points |
FAQ
Is the online protractor accurate?
Do I need to calibrate before measuring angles?
Can I move and rotate the protractor?
Related guides
Open the online ruler and start measuring
Free, no install, calibrate once and measure forever.
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