DeviTestOnline ruler (actual size)
A ruler in centimeters and inches that shows real sizes once you calibrate it with any bank card. It also estimates your screen size.
1. Calibrate with a bank card
Hold any bank or ID card against the screen. Move the slider until the blue box is exactly as wide as the card’s short edge.
Card short edge · 53.98 mm
2. Measure
Your screen (estimated)
Diagonal
Pixel density
Why calibration is needed
Browsers don't know the physical size of your screen, so a "centimeter" on one device can be a different length on another. Bank and ID cards are made to a fixed international size (ISO/IEC 7810 ID-1: 85.60 × 53.98 mm), which makes them a reliable reference you already have in your wallet.
Tips for accurate measurements
- Keep the browser zoom at 100% (Ctrl + 0 on a computer), or the scale will change.
- Calibrate separately on each device and in each browser.
- Place objects flat against the screen and look straight at them.
The screen size and pixel density are estimates based on your calibration. For exact numbers, compare with your device specs in the PPI calculator.