How the 1:1 actual-size ruler works
Every screen is made up of millions of LEDs or liquid crystals grouped into pixels. The key characteristic of any display is its pixel density — PPI (pixels per inch). Standard office monitors run at roughly 96–109 PPI, modern laptop screens range from 140–220 PPI, and smartphone screens can exceed 400–460+ PPI.
If a ruler image is displayed without accounting for the display's characteristics, one centimeter on a phone will appear 3–4× smaller than real life, and several times larger on a big TV screen. Our virtual ruler solves this programmatically: the algorithm reads the DPR (Device Pixel Ratio) scale factor, the actual viewport resolution, and hardware screen parameters.
For uncompromising 1:1 physical accuracy, two quick calibration methods are available:
- Credit card calibration: Any debit or credit card, driver's license, or loyalty card follows the ISO/IEC 7810 ID-1 standard and measures exactly 85.60 × 53.98 mm. Place the card against the on-screen outline, adjust the slider, and you get perfect 1:1 metrological accuracy.
- Screen diagonal calibration: Select your monitor's exact diagonal in inches (e.g., 13.3″, 15.6″, 24″, or 27″) and the system instantly calculates the correct scale for your screen.