Online ruler in actual size
Match the on-screen card to a real bank card, and the ruler is drawn at actual size in centimetres, millimetres or inches. The number is saved on this browser and display; calibrate again if you change the browser zoom or use another screen.
Your ruler appears here when you save a calibration.
Hold what you are measuring against the screen and read where it ends.
Calibrate your screen
A ruler is only true to size when it knows how big your pixels are. Match the on-screen card to a real bank card and save: the ruler appears above, and we remember it on this browser and display.
Hold a bank card flat against your screen and keep your browser zoom at 100%.
Move the slider to match your card, then save.
How it works
- Hold a bank card flat against your screen.
- Drag the slider until the on-screen card is as wide as the real one (on a phone, as wide as its short edge), then save.
- Pick a unit and hold what you are measuring against the ruler.
Calibrate for this browser and display, and again after you change your browser zoom or move to another display. The ruler hides itself if it notices during a visit, and the bank-card check above shows whether it is still right. It is an estimate, typically within a few percent, because the browser cannot read the real size of your screen.