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.
Centimeters and inches at actual size
⚠ Not calibrated — 30-second setup for true 1:1 size (click to expand)
Estimate (96 px/inch reference)Click or use arrow keys + Enter to mark two points and measure.
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.
Related tools
- Screen Size Comparison Compare phone, tablet, laptop and monitor screens as proportional overlays — or against your own screen. True-size mode shows devices at real physical size.
- PPI Calculator Calculate PPI from resolution and screen size. Instant results with the formula worked through your numbers, plus physical dimensions and dot pitch.
- What Is My Screen Size? Instantly see your screen resolution, viewport size, device pixel ratio and more. Live values that update as you resize, with a copyable debug report.
- Phone Screen Sizes Filterable phone screen size chart with display inches, resolution, PPI, aspect ratio and viewport for the iPhone, Galaxy S and Pixel models tracked here.