Online Ruler
Calibrated, true-to-size ruler in cm, mm and inches
How to use Online Ruler
- Calibrate once with a standard-size card or a known length.
- Place the object against the screen at the ruler’s zero mark.
- Read the size, or drag the markers to measure a distance.
About this tool
Measure small objects with a ruler on your screen in centimeters, millimeters and inches. Drag the two markers to read the distance between them.
Screens differ in size, so calibrate the ruler once: hold a standard bank or ID card against the screen and match the outline, or measure a line with a real ruler. The calibration is remembered on this device and adjusts itself when you zoom the page.
- Works on your device. Nothing is uploaded.
- Free, with no sign-up and no watermark.
- No limits on file count or size beyond what your device can handle.
Questions and answers
Is the online ruler accurate?
After calibration it is usually accurate to about half a millimeter. Without calibration, sizes are based on a standard screen and can be off by 10–30%.
Which cards can I use to calibrate?
Any card in the standard credit card size of 85.6 × 54 mm, such as a bank card, an ID card, a driver’s license or a loyalty card.
Do I need to calibrate again?
Only on a different screen. Page zoom is taken into account automatically.
Is Online Ruler free?
Yes. Every tool on ImgImage is free to use, with no sign-up, no watermark and no limit on how many files you process.
Does it work on my phone?
Yes. It works in any modern browser on phones, tablets and computers. Large files are processed faster on a computer.