Online Ruler Measurements is a free website that turns your screen into a ruler. You can measure small, flat objects in centimeters, millimeters, and inches without picking up a physical ruler.
What We Offer
Our main tool is an online ruler that works in any modern browser on a phone, tablet, or computer. It supports metric and imperial units, horizontal and vertical layouts, fullscreen mode, and dark mode. We also have a dedicated mm ruler page with an actual size chart and a converter between millimeters, centimeters, and inches.
Why Calibration Matters
Every screen has a different pixel density, so a ruler on screen is only close to real size after it is calibrated. Our tool offers several ways to do this: auto-detect, choosing your device, entering your screen diagonal, matching a standard credit card (85.60 x 53.98 mm, ISO 7810), or matching a real ruler. Once calibrated, the ruler is much closer to real size on that device.
Who This Site Is For
Students, crafters, tailors, designers, and anyone who needs a quick size check when a physical ruler is not nearby. For work that needs high precision, we recommend a certified physical measuring tool.
Our Approach
We aim to keep the tools simple, free, and easy to use on any device. We write clear instructions, and we explain the limits of on-screen measuring honestly. You can read more in our Disclaimer.
Get in Touch
Have feedback, a bug report, or a suggestion for a new tool? Email us at [email protected] or use the form on our Contact page.