CM Ruler: Actual Size Centimeter and MM Ruler Online
Metric ruler with millimeter ticks. Calibrate once and measure real cm and mm on your screen.
How to read a centimeter ruler
- Long numbered lines mark whole centimeters.
- The middle line between two numbers marks 5 mm, half a centimeter.
- Short lines mark single millimeters. There are 10 mm in each centimeter.
Example: the object ends 6 small lines after 3. That is 3.6 cm, or 36 mm. Switch to mm if you want the ruler numbered in millimeters. Drop two guides on the ruler edge and the label shows the distance to the nearest millimeter. More on reading a ruler.
Common small things in cm and mm
| Object | cm | mm |
|---|---|---|
| Bank card width | 8.56 | 85.6 |
| Bank card height | 5.40 | 53.98 |
| AA battery length | 5.05 | 50.5 |
| 1 euro coin | 2.33 | 23.25 |
| SIM card (nano) | 1.23 x 0.88 | 12.3 x 8.8 |
| Ring size 7 (inside diameter) | 1.73 | 17.3 |
Use the bank card to check your calibration. Step by step: calibrate with a credit card.
Centimeters, millimeters and inches
| cm | mm | inches |
|---|---|---|
| 1 | 10 | 0.39 |
| 2 | 20 | 0.79 |
| 5 | 50 | 1.97 |
| 10 | 100 | 3.94 |
| 15 | 150 | 5.91 |
| 20 | 200 | 7.87 |
Need inches? Open the inch ruler.
Frequently asked questions
How do I read a cm ruler?
Each numbered long line is one centimeter. The 9 small lines between them are millimeters, and the slightly longer middle line marks 5 mm. So 4 lines after the 7 cm mark is 7.4 cm or 74 mm.
Can I measure in millimeters?
Yes. Press mm to number the ruler in millimeters, or stay in cm and count the small ticks. Each tick is 1 mm.
Is this cm ruler actual size?
Yes, once you calibrate it with a bank card, your device model or your screen diagonal. The status line shows when it is calibrated.
How many centimeters does a phone screen show?
Most phones show about 13 to 15 cm on the long edge. Use the left edge or Vertical mode for the longest ruler.
How do I convert cm to inches?
Divide centimeters by 2.54. For example 10 cm is about 3.94 inches. Or switch the ruler to inches with one tap.