Online ruler help center

Measurement guides for online rulers

Use these guides to calibrate an on-screen ruler, read inch and metric marks, calculate screen scale, and convert measurements after you read them.

Start measuring

Open the browser ruler and measure in centimeters, millimeters, or inches.

Learn inch fractions, centimeter marks, millimeter ticks, and common reading mistakes.

Use a credit card, screen diagonal, or known reference object to set actual size.

Estimate CSS pixels per inch and pixels per millimeter for your display.

Convert inch fractions, decimal inches, centimeters, and millimeters.

Convert centimeters to inches with a formula and reference chart.

Convert inches to centimeters with a formula and reference chart.

Convert millimeters to inches with a formula and reference chart.

How precise a screen ruler is and what changes the result.

When to use a screen ruler and when to reach for a physical one.