Digital tool
Digital Protractor – Free Online Angle Measurement
The digital protractor measures any angle directly on screen — no install, no sign-up. Place the protractor center on the vertex, align the baseline ray to 0°, and drag the second ray. Read precise interior and reflex angles in degrees or radians, with snap, grid, and image overlay for photos, diagrams, blueprints and screenshots. Free and private in your browser.
Free•No sign-up•Works in browser•Image stays local
Updated Online Protractor
Keyboard: Tab handles, arrows nudge 1px center / 1° ray (Shift 10px / 5°), R reset, G grid, L lock baseline, Z undo, Shift+Z redo, +/- zoom. Endpoint magnifier shows while dragging. Drag center, baseline ray, second ray. Snap preview before commit. Image stays local — never uploaded. Press Esc to exit fullscreen.
Camera stays local — capture is processed in your browser
Digital reading updates live as you drag. Toggle degrees/radians and precision 0–2 decimals. Accuracy notes
How to measure — 3 steps
- 1Place the center on the vertex
Drag the glowing center to the point where the two rays meet. Use crosshair and the magnifier that appears while dragging for precise placement.
- 2Align the baseline
Drag handle A to the first edge at 0°. Lock baseline if you want it fixed while adjusting the second ray. Try snap 5° or 15° for common angles.
- 3Read & copy the digital result
Drag handle B to the second edge — the chip shows interior ≤180° and reflex 360°−inner. Copy, toggle reflex, or switch degrees/radians.
When to use a digital protractor
- Photos & screenshots: measure angles on images, diagrams, blueprints and homework photos without printing.
- DIY & carpentry: check miter, bevel and joint angles from a reference photo.
- Design & geometry: verify interior/exterior angles and three-point angles for study.
Semantic: vertex is the intersection of two rays; interior is the smaller side, reflex the larger (exterior) side.
Accuracy & limitations
We avoid unverified ± claims. The digital math is exact for your points; appearance is not.
- Photo perspective and lens distortion skew the 2D projection vs the real 3D angle.
- Screen scale/zoom and touch parallax affect placement — use crosshair, grid and magnifier.
- For safety-critical work, verify with a calibrated physical protractor. Read accuracy guide →
Privacy
Images are processed locally via Blob URL / FileReader — never uploaded, never stored server-side. Revoked on clear. No account, no tracking of image contents.
FAQ
What is a digital protractor?
A digital protractor is a software protractor that measures angles on screen. Place the protractor center on the vertex where two rays meet, align the baseline to 0°, and read the interior angle instantly — no physical tool needed.
How is it different from a physical protractor?
You drag instead of holding plastic. The digital version adds snap, grid, reflex toggle, degrees/radians switch, and image overlay for photos, diagrams, blueprints and screenshots — all in the browser.
Can I use it on a photo?
Yes — upload a PNG, JPG or WebP photo. The image is processed locally via Blob URL and never leaves your device. Pan, zoom and rotate the photo, then measure the 2D angle you see. See measure-angle-from-image for details.
How accurate is the digital measurement?
The angle math is precise for the points you place. Apparent accuracy depends on photo perspective, lens distortion, screen scale and touch placement. For construction or safety-critical work, verify with a calibrated physical instrument.