Actual-size online ruler
Open the browser ruler and measure in centimeters, millimeters, or inches.
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
CM ruler online
Measure in centimeters on screen and learn how cm marks relate to millimeter ticks.
MM ruler online
Use millimeter marks for small metric measurements after careful calibration.
Inch ruler online
Read inch fractions and use a calibrated on-screen inch ruler.
Online measuring tape
Scroll along a longer calibrated tape in inches or centimeters.
How to read a ruler
Learn inch fractions, centimeter marks, millimeter ticks, and common reading mistakes.
How to read a ruler in mm
Step-by-step guide to reading millimeter marks on a metric ruler.
Actual-size references
2 mm actual size on screen
Open a calibrated 2 mm visual guide with millimeter, centimeter, and inch conversions.
4 mm actual size on screen
Open a calibrated 4 mm visual guide with millimeter, centimeter, and inch conversions.
5 mm actual size on screen
Open a calibrated 5 mm visual guide with millimeter, centimeter, and inch conversions.
2.5 cm actual size on screen
Open a calibrated 2.5 cm visual guide with millimeter, centimeter, and inch conversions.
3.2 cm actual size on screen
Open a calibrated 3.2 cm visual guide with millimeter, centimeter, and inch conversions.
5 cm actual size on screen
Open a calibrated 5 cm visual guide with millimeter, centimeter, and inch conversions.
10 cm actual size on screen
Open a calibrated 10 cm visual guide with millimeter, centimeter, and inch conversions.
Calibrate the screen
Online ruler calibration guide
Use a credit card, screen diagonal, or known reference object to set actual size.
Screen PPI calculator
Estimate CSS pixels per inch and pixels per millimeter for your display.
Convert measurements
Ruler measurement converter
Convert inch fractions, decimal inches, centimeters, and millimeters.
CM to inches converter
Convert centimeters to inches with a formula and reference chart.
17 cm to inches
Find the precise 17 cm result, rounding details, and nearby conversions.
Inches to cm converter
Convert inches to centimeters with a formula and reference chart.
MM to inches converter
Convert millimeters to inches with a formula and reference chart.
Understand and compare
Is an online ruler accurate?
How precise a screen ruler is and what changes the result.
Online ruler vs physical ruler
When to use a screen ruler and when to reach for a physical one.