Preparing tool
How to use Online Ruler
- Place a bank card (or a coin) on the screen and drag the slider until the dashed outline matches it exactly. Or enter your screen size in inches.
- Choose centimetres or inches and lay your object along the ruler; tap or drag on it to place a marker and read the length.
- Switch to the protractor, put the centre dot on the corner, line up the base and drag the red arm to read the angle.
What are the limits of Online Ruler?
Screens do not tell websites their real size, so calibrate once per device and keep the page zoom at 100%. Accuracy depends on how carefully you match the card; for anything critical, use a physical ruler.