Read · compare · verify
Reading guide
Worked example7 cm + 3 mm = 7.3 cm
| Reading | Equivalent | How to read it |
|---|---|---|
| 1 cm | 10 mm | One numbered interval |
| 2.5 cm | 25 mm | Two intervals plus the middle tick |
| 7.3 cm | 73 mm | Seven intervals plus three small ticks |
| 10 cm | 100 mm | Ten intervals; only if the screen span fits |
Read centimeters without losing the small marks
A centimeter ruler divides each numbered interval into ten millimeters. The longer middle tick is half a centimeter, or 5 mm. If an object ends three small ticks beyond 7, its length is 7.3 cm, not 7.03 cm. The target guide starts at the screen scale’s origin, so align the object with that origin rather than with the bezel of your device.
A centimeter ruler online for small, flat objects
Paper tabs, craft pieces, buttons, and other objects that fit beside a screen are useful candidates. Type the expected length above to compare it with the object, or tap the canvas to pin an endpoint. You can move a pinned guide and remove it with a click or Delete. For an object that starts away from the origin, subtract its starting reading from its ending reading.
When 10 cm does not fit
The visible range depends on your calibrated screen, not on the browser’s default pixel density. A narrow phone may not display ten physical centimeters across its width. Choose a vertical edge or rotate the device, then recheck calibration. Do not shrink the ruler to make it fit: that would change the physical size of every centimeter.
How this ruler works
The scale uses your current calibration in CSS pixels per inch. Metric ticks divide that density by 25.4; inch ticks divide it by 16. Conversions use the exact definition 1 inch = 25.4 mm. The target keeps its entered length rather than stretching to fill the display.
Keep browser zoom at 100%, verify with a known reference, and recheck after changing screens. Inputs stay in your browser; no camera, account, or upload is required. For critical dimensions, use a suitable calibrated physical instrument.
Methodology, calibration help, and measurement support: Accuracy methodology · Calibrate screen · Contact us. Unit definitions: NIST.