Turn on a ruler in the bar above to start measuring
Place a ruler on any edge.

Choose an edge below or in the toolbar above.

📏 Real ruler on screen

Online Ruler — Real Size

Place rulers on the screen edges and measure in cm, inches or pixels. ← Back to Protractor

How to calibrate

  1. Click 📐 Calibrate and choose Auto, Device, Diagonal or Card.
  2. Keep browser zoom at 100%.
  3. Done — calibration is saved on your device.

Shortcuts: G guides · C crosshair · F fullscreen · 1/2/3/4 units · D theme · Esc clears · hold a guide to delete.

FAQ

Is the online ruler accurate?

Close after calibrating on your screen at 100% browser zoom. Without calibration we use an estimate and values may be off.

Which calibration methods exist?

Device auto-detection, model list, screen diagonal in inches and the classic physical card on the screen edge.

How do I add measuring guides?

Turn on the ⌖ Guides button and tap near any screen edge to drop a green line. Drag to move, double-tap or long-press to delete.

How to measure a real object with the phone?

Tap 📱 Phone: the screen becomes an edge ruler. Hold the phone side against the object and fine-tune +/− with a card.

Is my data saved?

Only in your browser. Nothing is sent to any server, no account, no upload.