Measure on screen in centimeters and inches — horizontal, vertical, or a corner ruler.
How to use this ruler
Measure anything on your screen without a physical ruler. Pick cm / mm or inches, choose Horizontal, Vertical, or Both, press Measure, then click and drag along the ruler. Release to read the distance.
In Both mode the rulers share one origin point at the top-left corner, so you can measure across width and height together.
Getting real-size accuracy
The ruler uses your screen's CSS pixels, which is close to real size at 96 DPI but can vary by display. To make it exact: measure a real object on screen (a credit card is 8.56 cm wide), enter its true length, and press Apply.
Scale factor = measured pixels ÷ true length (cm)
After calibration every mark is rescaled so 1 cm on screen equals 1 real centimeter.
Tips
- Use the vertical ruler to measure heights or on-screen paper edges.
- Read mm directly under cm mode — each small tick is 1 mm.
- Press Reset to clear the measurement and restore the default scale.
How do I measure something without a physical ruler?
Use the on-screen ruler: pick cm/mm or inches, choose an orientation, press Measure, then click and drag across the object you're measuring. The readout shows the distance.
How accurate is an online ruler?
Out of the box it is accurate in CSS pixels (96 DPI). For physical accuracy, calibrate it against a real object such as a credit card (8.56 cm wide) using the calibration box.
How do I calibrate the ruler to real size?
First measure the object on screen with the Measure tool, then enter its true length in centimeters and press Apply. The ruler rescales to match real size.
How many millimeters are in a centimeter?
There are 10 millimeters in 1 centimeter, so 1 cm = 10 mm.
Can I measure inches on screen?
Yes. Switch from cm/mm to inches at the top of the ruler. Inches are shown to two decimal places with 1/8-inch tick marks.