Centimeter Ruler Online (cm / mm, Actual Size)
A true-size metric ruler with millimeter ticks. Calibrate once and measure in centimeters and millimeters; the readout also shows inches.
How to measure in centimeters
- Set zoom to 100%. Press Ctrl + 0 (⌘ + 0 on Mac). After calibrating, the ruler corrects itself automatically if you zoom.
- Press Calibrate. Hold a credit card, debit card, ID or gift card flat against the screen and resize the on-screen card until it matches. No card? Use a coin, a dollar bill, a sheet of A4 or Letter paper, your screen size, or pick your device from the list.
- Save. Your calibration is stored on this device only, so next time the ruler opens at true size.
Reading cm and mm
Numbers mark whole centimeters. Ten small ticks make one centimeter; each tick is 1 mm, and the medium tick is 5 mm. If an object ends 7 ticks past the 12, it is 12.7 cm (127 mm) long.
cm to inches table
| Centimeters | Millimeters | Inches |
|---|---|---|
| 1 cm | 10 mm | 0.394 in |
| 2 cm | 20 mm | 0.787 in |
| 3 cm | 30 mm | 1.181 in |
| 4 cm | 40 mm | 1.575 in |
| 5 cm | 50 mm | 1.969 in |
| 6 cm | 60 mm | 2.362 in |
| 7 cm | 70 mm | 2.756 in |
| 8 cm | 80 mm | 3.150 in |
| 9 cm | 90 mm | 3.543 in |
| 10 cm | 100 mm | 3.937 in |
| 11 cm | 110 mm | 4.331 in |
| 12 cm | 120 mm | 4.724 in |
| 13 cm | 130 mm | 5.118 in |
| 14 cm | 140 mm | 5.512 in |
| 15 cm | 150 mm | 5.906 in |
| 16 cm | 160 mm | 6.299 in |
| 17 cm | 170 mm | 6.693 in |
| 18 cm | 180 mm | 7.087 in |
| 19 cm | 190 mm | 7.480 in |
| 20 cm | 200 mm | 7.874 in |
| 21 cm | 210 mm | 8.268 in |
| 22 cm | 220 mm | 8.661 in |
| 23 cm | 230 mm | 9.055 in |
| 24 cm | 240 mm | 9.449 in |
| 25 cm | 250 mm | 9.843 in |
| 26 cm | 260 mm | 10.236 in |
| 27 cm | 270 mm | 10.630 in |
| 28 cm | 280 mm | 11.024 in |
| 29 cm | 290 mm | 11.417 in |
| 30 cm | 300 mm | 11.811 in |
Need more? See the full cm to inches conversion chart or use the converter:
Print a metric ruler
Make a 30 cm printable ruler, a 15 cm pocket ruler, or a 1 m ruler in parts for A4 or Letter paper.
FAQ
How long is 1 cm on my screen?
After calibration, the gap between two numbered lines on the cm scale is exactly 1 centimeter, and each small tick is 1 millimeter.
How many millimeters are in a centimeter?
10 millimeters. 1 meter is 100 cm or 1000 mm.
How do I convert cm to inches?
Divide by 2.54. For example, 10 cm ÷ 2.54 = 3.94 inches.
Can I measure millimeters accurately on a screen?
Yes. On a calibrated screen the ruler is accurate to about half a millimeter. Zoom the browser back to 100% before calibrating.
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