About Exact Ruler
Exact Ruler turns the screen of your phone, tablet or computer into a ruler you can trust. Hold a small object against the screen, line it up with the 0 mark and read its size in centimeters, millimeters, inches or pixels.
Why it exists
Most online rulers draw an inch as 96 screen pixels, because that’s what web browsers assume. Real screens don’t work that way. Depending on your device and display settings, an uncalibrated online ruler can be off by 10 to 40 percent, which makes it useless for anything that matters, like a ring size or a replacement screw.
Exact Ruler is built around getting that number right. It recognizes many devices automatically and lets you calibrate any screen in seconds by matching a bank card, which has the same standard size everywhere in the world.
What you can do with it
- Measure in centimeters with millimeter marks, in inches down to 1/16, or in CSS pixels.
- Place rulers on any edge of the screen, drop guides and read the distance between them.
- Measure width and height at once with the measuring box.
- See exactly how big a length is, such as 5 cm or 2 inches, before buying something online.
Free and private
Exact Ruler is free to use, with no account and nothing to install. It runs entirely in your browser. Your calibration is saved on your own device and is never sent to us. The site is supported by advertising; you can read how that works in our privacy policy.
Get in touch
Found a device that isn’t listed, a measurement that seems off, or an idea for a feature? Contact us. Reports like these are how the ruler gets more accurate.