What is it?
The Online Ruler shows a real-size ruler in centimetres and inches on your phone or computer screen, once calibrated.
Who is it for?
Anyone needing a quick measurement without a scale: ring sizes, screws, paper sizes, product sizes for online orders, and children’s homework.
How to use it
- Calibrate once with a bank card or your screen size.
- Place the object on the screen at zero.
- Read the length in cm or inches.
Calibrate it first
- Tap Make the ruler exact for this screen (calibrate).
- Hold any bank / debit / ID card (85.6 × 54 mm) against the screen and drag the slider until the box matches the card. Every standard card has this size.
- Or type your screen size (the diagonal, e.g. 15.6) and tap Use screen size.
- After calibrating once, the ruler is saved for this device. Reset clears it.
Measuring
Tap or drag on the ruler to measure. Place small objects flat on the screen, against the zero mark. For long objects, measure in steps and add them up.
It’s not accurate
- Browser zoom must be 100%. Press Ctrl + 0 on a computer; on a phone, zoom out fully.
- Calibrate again after changing the display scaling in Windows settings or moving to another monitor.
- Screen size typed from memory is often rounded. The card method is more accurate.
Good for rings, screws, buttons and paper sizes; for building work use a real tape.
Open the tool: Online Ruler
Still stuck?
Contact support. Tell us which tool or page you were using, what you tapped, what you saw, and your phone or computer and browser (for example: Android phone, Chrome). We reply by email.
Questions, or an error not listed here?
Tell us in the comments: what you were doing, the exact message you saw, and your device and browser. We read every comment and add new fixes to this article.