Online Ruler
Tip: hold a real ruler or credit card (85.6mm wide) to the screen and adjust until the marks line up.
Measure small objects right against your screen with an on screen ruler marked in both centimeters and inches. Because every display has a different pixel density, the ruler includes a calibration slider: hold a real credit card or a physical ruler against the screen and adjust the slider until the markings match, and from then on your measurements will be accurate. This is handy for a quick measurement when you cannot find a tape measure, for checking a length while shopping online, or for design work. Keep in mind that accuracy depends entirely on calibrating for your specific monitor, and that very large objects will not fit. Everything runs locally in your browser, and your calibration setting is remembered so you only have to set it once.
How to use Online Ruler
- Place a known-size object like a card against the screen.
- Adjust the calibration slider until the ruler matches it.
- Choose centimeters or inches.
- Measure your object against the ruler.
Frequently asked questions
Can it show real-size measurements?
Yes. A calibration slider matches your display DPI so the on-screen ruler reflects real centimeters and inches.
Why do I need to calibrate it?
Screens vary in pixel density, so calibrating against a known object makes the ruler accurate for your specific display.
Which units does it show?
It shows both centimeters and inches so you can measure in whichever unit you prefer.
What is Online Ruler?
Measure small objects right against your screen with an on screen ruler marked in both centimeters and inches. Because every display has a different pixel density, the ruler includes a calibration slider: hold a real credit card or a physical ruler against the screen and adjust the slider until the markings match, and from then on your measurements will be accurate.
Is Online Ruler free to use?
Yes. Online Ruler is completely free, with no sign-up and no usage limits.
Does Online Ruler work in a web browser?
Yes. Online Ruler runs in any modern web browser. There is nothing to download or install.
Is my data private with Online Ruler?
Yes. Online Ruler runs entirely on your device in your browser, so nothing you enter is uploaded to a server.
Badge
Link this tool from a README, doc or site. The badge links back to this page.
[](https://yourhack.ai/online-ruler)