Online CM Ruler with Millimeter Ticks

A clean metric ruler for centimeter and millimeter measurements. Calibrate once for real physical size, then place a small object against the zero mark and read the scale.

Calibration is stored only in this browser.
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Drag across the ruler to measure a span.
⌨ Keyboard shortcuts

C cm · I inch · P px · R rotate · F fullscreen · G guides · X crosshair · A angle · D dark · 4 four edges

Calibrate1Ruler

Match a standard bank card width (85.60 mm) to the guide below.

85.60 mm

Read centimeters and millimeters clearly

The metric scale marks every millimeter and gives a stronger mark at 5 mm and each full centimeter. One centimeter equals 10 millimeters, so a point three small ticks after 4 cm is 4.3 cm, or 43 mm.

Calibrate before measuring a physical object

Without calibration, the browser can only start from a generic display assumption. Use the bank-card reference or the screen-diagonal method so the on-screen centimeter matches a real centimeter on the display in front of you.

Good uses for a CM ruler

  • Labels, cards, stickers and small paper pieces.
  • Craft materials, screws, connectors and desk objects that fit safely against the screen.
  • Quick school or household checks where a physical ruler is not nearby.

Avoid common metric measuring errors

Align the object with the zero line, keep it parallel to the ruler and do not change browser zoom after calibration. If you switch to another monitor, calibrate that display separately.