Online Ruler — cm & inches

Hold anything up to your screen. No setup required — calibrate only if you want extra precision.

Using an estimated scale — close, but not exact.

Match the box to a real card

Grab any standard bank or ID card and hold it against the screen. Drag the orange dot until the blue box is exactly the same width as the card.

Compare two lengths

vs

Printable ruler

Skip the screen entirely — download a true 1:1 scale ruler to print at home.

Units:

How to use the online ruler

The ruler above shows an estimated real-world scale as soon as the page loads — most people never need to touch calibration. If you want pixel-accurate measurements:

  1. Click "Calibrate with a card."
  2. Hold a bank or ID card against your screen next to the blue box.
  3. Drag the orange dot until the box matches the card's real width.
  4. Save — your browser remembers this the next time you visit.