Online Actual Size Ruler
A precise, calibrated ruler on your screen. Use a credit card to calibrate your display for 100% accuracy.
Waiting for calibration...
How to use this online ruler
Most screens have different pixel densities (PPI), which means "100 pixels" looks different on a phone versus a desktop monitor. To make this ruler accurate, we need to calibrate it.
- Click "Calibrate" if the modal doesn't appear automatically.
- Grab a standard credit card (or any card from your wallet).
- Adjust the slider until the blue box on the screen matches the physical card width exactly.
- Click "I'm Calibrated".
Need a real ruler?
Download our Printable Ruler PDF. Perfect for measuring wrists, curved surfaces, or when you just can't find a metal ruler.