Actual size · No ads · 100% free
Online Ruler
A real-size ruler on your screen. Horizontal or vertical, centimeters and inches side by side, inch fractions, and one-time calibration for accurate results on any device.
Tip: click and drag across the ruler to measure. The readout shows centimeters, decimal inches and the nearest 1/16″ fraction. Your unit, orientation and calibration are saved automatically.
Calibrate for actual size
Screens have different pixel densities. Calibrate once and the ruler will show true real-world sizes.
Method 1: Match a real object
Pick an object you have at hand, hold it against the box, then drag the blue handle (or use the slider) until they match exactly.
Method 2: Screen size
Enter your screen's diagonal size in inches (for example 13.3, 15.6 or 27) and we'll compute the density.
Auto-detect uses your display's reported pixel density. It is a good starting point; fine-tune with a real object for maximum accuracy.
Truly accurate
Calibrate with a bank card, banknote, coin, your screen size, or automatically. The ruler then matches real-world size on phones, laptops and monitors.
Metric & imperial together
Centimeters with millimeter ticks, inches down to 1/16″, or both scales at once like a real ruler. Measurements show cm, decimal inches and inch fractions.
Any direction, any device
Switch between horizontal and vertical orientation, go fullscreen, and measure with mouse or touch. No ads, no tracking, everything runs in your browser.
Frequently asked questions
How accurate is this online ruler?
After calibration it is accurate to within a fraction of a millimeter. Without calibration it uses your display's reported pixel density as a starting estimate, which is close on most devices.
How do I calibrate the ruler?
Hold a credit card, dollar bill or coin against the reference box and drag the blue handle until the sizes match, or enter your screen's diagonal size in inches. Your setting is saved for next time.
Can I measure vertically?
Yes. Switch the orientation to Vertical and the ruler rotates so you can measure the height of objects held against your screen. Drag up or down to measure, just like in horizontal mode.
Does it show inch fractions?
Yes. Every measurement shows centimeters, decimal inches and the nearest 1/16″ fraction, so you can read it like a tape measure.
Does it work on phones and tablets?
Yes. The ruler works with touch input, so you can drag to measure with your finger. Calibrate with a credit card or coin for best results on mobile screens.
Is it really free?
Completely. No ads, no accounts, no data collection. All measuring happens locally in your browser.