Online CM Ruler: Measure in Centimeters & Millimeters
Use the on-screen ruler to measure straight lengths in centimeters and millimeters. Switch to inches or pixels when needed, and calibrate the display when you need the scale to represent a physical size.
Quick Usage
Choose your unit
Use cm for everyday lengths and mm when you need smaller divisions. You can also switch to inches or pixels from the tool controls.
Calibrate for physical size
When you are measuring a physical object, calibrate the display with a known reference before relying on the cm, mm, or inch reading.
Align and read
Start one edge at zero, keep the object aligned with the ruler, and read the other edge. For a diagonal or point-to-point distance, use the Line controls in the measurement area.
Centimeters and Millimeters
One centimeter contains 10 millimeters. Use centimeters for larger everyday lengths and millimeters when you need a finer reading.
When Calibration Matters
CSS defines 1 inch as 96 CSS pixels, but that is not a measurement of the physical size of your particular display. Calibrate when you want the ruler's cm, mm, or inch scale to represent a physical length.
Measuring a Physical Object
After calibration, place the object along the ruler and align its starting edge with zero. Keep the object as straight and flat as practical, then read where the other edge meets the scale.
Know the Limits
This ruler is useful for quick checks and everyday sizing. Physical results can be affected by calibration, browser zoom, display scaling, viewing angle, and small alignment errors. For measurements where a small error has important consequences, verify the result with an appropriate physical measuring instrument.
Frequently Asked Questions
cm、mm、実寸サイズ、画面での長さ測定に関するよくある質問。