Calibrate this free screen ruler to 1:1 actual size, then measure objects in centimetres, millimetres and inches on any device.
Tap the ruler to place A and B, or drag either marker. Arrow keys move a focused marker by 0.5 mm; Shift + Arrow moves it by 5 mm.
A browser knows its pixel dimensions, but not the physical size of each pixel. That is why an uncalibrated virtual ruler is only an estimate. A standard ID-1 bank or credit card is 85.60 × 53.98 mm, making it a convenient reference on almost any device. Once matched, the PPI value is saved and this screen ruler displays at 1:1 actual size.
The metric edge works as both a centimetre ruler and millimetre ruler, marking every millimetre and labelling each centimetre. The inch ruler can be divided into eighths, sixteenths or thirty-seconds. The live A–B result shows cm, mm, decimal inches and the nearest selected fraction together.
Use the ruler on a phone or tablet in vertical mode, or open it full screen on a laptop or desktop computer. On a narrow display the card guide uses the 53.98 mm short edge. Recalibrate after changing browser zoom, display scaling, device or monitor.
The ruler is drawn and calculated entirely in your browser. No object, measurement or calibration value is uploaded. Your saved calibration remains only in local browser storage until you reset it or clear site data.
After careful credit-card calibration, this actual-size measuring tool is suitable for everyday objects. Screen pixels, rounded display edges and viewing angle still limit precision, so use a physical ruler or calipers for safety-critical or manufacturing measurements.
It becomes actual size after calibration. Before calibration it uses the browser reference of 96 CSS pixels per inch, which may differ from the physical screen.
Most bank and credit cards follow the ISO/IEC 7810 ID-1 size of 85.60 × 53.98 mm, giving you a widely available physical reference.
Yes. The ruler displays metric and imperial scales together, and the A–B result includes cm, mm, decimal inches and fractions.
Yes. Use horizontal or vertical mode and full screen. Card calibration is recommended because mobile pixel density varies greatly.
Yes. Calibrate once on that display, keep the same browser zoom, then place an object against the screen and use the two markers to measure it.
Yes. Keep the zoom level used for calibration, usually 100%, or calibrate again after changing it.
No. Measurement and calibration calculations stay in your browser.