About Us
The team behind Online Ruler
Online Ruler started with a simple frustration: almost every "ruler" found on the web guesses your screen size. A default 96 PPI assumption is wrong for most modern displays — from budget monitors to high-density phones. We built a tool that actually measures at real, physical size by calibrating to your specific screen.
Our Mission
We want accurate measurement to be free and instant. No app download, no sign-up, no ads watching you. Just open the page, calibrate once, and measure in inches, centimeters, or millimeters with confidence.
What Makes Us Different
- Calibrated accuracy — four calibration methods (auto-detect, device selection, screen diagonal, and credit-card alignment) so 1 cm on screen equals 1 real centimeter.
- Privacy-first — every measurement is computed locally in your browser. Nothing is uploaded.
- Full toolkit — edge rulers, guide lines, a box/area tool, an angle protractor, labels, crosshair, and an optional camera mode.
- Open and lightweight — fast to load on any device, from desktop to phone.
How It Works
The tool reads your screen's pixel density, lets you fine-tune it, and then renders tick marks that match true physical dimensions. Switch units anytime; the marks rescale automatically. Your calibration is remembered on your device for future visits.
Our Values
- Useful over clever. The tool should just work when you need it.
- Private by default. If we don't need your data, we don't take it.
- Accessible. Keyboard shortcuts, dark mode, and responsive design for every device.
Get in Touch
Have feedback, a feature idea, or a calibration that looks off? We'd love to hear from you on our contact page.