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How to read a centimeter ruler
Every numbered tick is one centimeter. The slightly longer tick halfway between the numbers marks 5 mm, and each short tick is 1 millimeter. To read a length, count the whole centimeters, then add the millimeters after the last number: three short ticks past the 6 is 6.3 cm, or 63 mm.
Quick metric conversions
- 1 cm = 10 mm = 0.3937 in
- 1 mm = 0.03937 in (about 1/25 inch)
- 2.54 cm = 1 inch exactly
- 30 cm ≈ 11.81 in, roughly a school ruler
Make it precise
Tap the ruler to get a reading to a hundredth of a centimeter, switch to inches any time, or open full screen to measure a diagonal. For the best result, reset browser zoom to 100% and use the credit card calibration.