1Ruler

Actual Size Ruler: Set the Screen to Real Scale

Real-size measurement begins with calibration. Verify the scale before trusting centimetres or inches on a new screen.

Calibration is stored only in this browser.

Drag across the ruler to measure a span.

What “actual size” means

After calibration, the distance between two marks on the display is intended to match the same physical distance in the real world. Before calibration, the ruler is only an estimate.

Best home calibration method

A standard ID-1 bank card is 85.60 mm wide. Match the on-screen reference to a physical card without pressing hard on the display. If you prefer not to place a card on the screen, enter the display diagonal from the manufacturer specification.

Verify after changes

Switching monitors, changing operating-system scaling or altering browser zoom can invalidate an old calibration. Recheck against a known object before precision matters.

Questions people ask before measuring

What makes a ruler “actual size”?

The scale must be matched to the physical display you are looking at. A saved calibration tells 1Ruler how many browser pixels correspond to a real inch on that screen.

Should I recalibrate after changing display zoom?

Yes. If browser zoom, system scaling, monitor or device changes, verify the scale again. 1Ruler warns when the saved display scale no longer matches the current one.