Online Ruler (Actual Size)
A ruler on the screen is only accurate once it knows the real size of your pixels. Calibrate it once by holding a credit card against the screen, or by typing the screen diagonal, and the ruler shows true centimetres and inches. Click or drag on the ruler to measure a length.
Calibrate
1. Hold a card (85.60 × 53.98 mm) against the blue rectangle and move the slider until it is exactly the same width.
2. Or type the screen diagonal in inches:
How to use it
- Hold a bank card, ID card or any card of the standard size against the blue rectangle and move the slider until they match; then click Use this size.
- Or type the diagonal of your screen in inches, as in the product specifications.
- Place the object at the left edge of the ruler and click where it ends to read the length.
Frequently asked questions
Why does the ruler need calibration?
Browsers use a fixed 96 pixels per inch, but real screens range from about 90 to more than 450 pixels per inch. Without calibration the centimetres on the screen can be much bigger or smaller than real ones.
Which card can I use?
Any card in the ID-1 format of the ISO/IEC 7810 standard: credit and debit cards, most ID cards and driver's licenses. They all measure 85.60 × 53.98 mm.
Is the calibration kept?
Yes, in this browser and for this screen size. On another monitor or after changing the display scaling, calibrate again. The browser zoom must be at 100%.
🖥️ What Is My Screen Resolution?
⚡ Refresh Rate Test (Hz)
🖱️ Mouse Test
⏱️ Reaction Time Test
🔊 Decibel Metre
🥁 Tap Tempo – BPM Counter
🖥️ Dead Pixel Test
🎹 Keyboard Test