Online Ruler in Inches: Measure in Inches
A precise inch ruler that works right in your browser, scaled to your device's real screen size.
OnScreenRuler's inch ruler turns your screen into a real, to scale measuring tool, perfect when you need a quick measurement and don't have a physical ruler on hand. It's calibrated to your exact device so the inch markings match true size.
For unlisted devices, calibrate manually using your screen's diagonal size or a standard credit card, which is always 3.37 inches wide.
How to Use the Online Ruler
- Choose an edge โ click Left, Right, Top, or Bottom above to pin the ruler to that edge of your screen.
- Switch units โ use the "Also measure in" links to open the cm, inch, mm, or px version of this ruler.
- Check the status banner โ green means your device was auto-detected and the ruler is accurate. A yellow banner means calibration is needed.
- Calibrate if needed โ click Calibrate and pick your device, enter your screen's diagonal size, or use a standard credit card.
- Measure โ place any object against the ruler edge. Hover for a live coordinate readout. Use Fullscreen for maximum measuring area.
How to Calibrate for Accurate Measurements
Accuracy depends on your screen's PPI being correctly set. There are three reliable ways to calibrate:
- Pick your device โ select your exact phone, tablet, or laptop model for the factory-precise PPI.
- Screen diagonal โ find your screen's diagonal size (printed on the box or searchable by model name) and enter it in the Calibrate panel. Works for any screen.
- Credit card calibration โ place any standard bank or credit card flat against the blue guide. All ISO 7810 cards are exactly 85.6 mm wide. Drag the slider until the guide matches the card edge.
Your calibration is saved in your browser and restored on your next visit.
Frequently Asked Questions
How do I measure in inches online?
Open onscreenruler.com, let the tool auto-detect your device, or calibrate manually, then hold your object against the on-screen inch ruler.
How long is 7 inches on this ruler?
Once calibrated, count to the 7 mark. Seven inches is roughly the length of a dollar bill plus about half an inch, a handy real world check if you want to verify your calibration.
How accurate is this inch ruler?
Once calibrated, accuracy is typically within 1 to 2 percent.
Can I switch units?
Yes, use the unit links on this page to open the cm or mm version anytime.