Online Ruler — Actual Size
A real-size ruler on your screen, in centimeters and inches. Calibrate once with any bank card for true 1:1 accuracy.
⚠ Not calibrated — 30-second setup for true 1:1 size (click to expand)
Estimate (96 px/inch reference)Click the ruler to mark two points and measure the distance.
Frequently asked questions
› How accurate is this online ruler?
After calibration, it is accurate to within about 1% — limited only by how precisely you match the card outline. Without calibration, browsers can't know your display's physical size, so the ruler falls back to a rough estimate.
› Why do I need to calibrate with a bank card?
Web browsers report sizes in pixels but don't reliably expose the physical dimensions of a display. A bank card has an internationally standardized width (85.60 mm, ISO/IEC 7810 ID-1), making it a measuring reference almost everyone has at hand.
› Is the calibration saved?
Yes, in your browser's local storage on this device. It also unlocks true-size mode in our screen size comparison tool. Nothing is sent to any server.