A free browser ruler that turns any display into an accurate measuring tool — calibrated to your exact screen, in centimeters, millimeters, or inches.
Measuring something shouldn’t require digging through a drawer for a ruler that’s never where you need it. We built OnlineRuler because we kept running into this exact problem — and most online alternatives we found were either inaccurate, cluttered with ads, or overcomplicated. OnlineRuler is fast, simple, and accurate by default.
Everything you need for on-screen measuring, calibrated to your device and nothing you don’t.
cm · mm · in
Switch instantly between centimeters, millimeters, and inches depending on what you’re measuring.
1:1
Calibrate once so 1 cm on screen equals exactly 1 physical centimeter — no guessing, no drift.
↕ ↔
Display the ruler along whichever edge fits what you’re measuring.
100%
Extend the ruler across the entire screen for larger objects.
0.0
Clear a measurement instantly and start the next one with zero friction.
∞
Every modern browser, every device — no download, no sign-up, no app.