A precise, calibratable virtual ruler — measure objects in real size on your screen.
It's a ruler that lives on your screen, drawn at real size so you can measure small things — a screw, a key, a bead, a coin, a slot in a phone tray — whenever the actual ruler is somewhere you aren't. Hold the object against the screen and read off the length, in centimeters, millimeters, or inches. You can lay it flat across the screen or stand it up vertically for taller items.
The honest catch with any on-screen ruler is that every display packs a different number of pixels into an inch, so the same line of pixels is physically bigger on a desktop monitor than on a phone. We handle that with a quick calibration: hold any bank or ID card — they're all the same 85.6 mm wide by international standard — against the screen, drag a slider until the on-screen card matches it, and from then on the ruler is true to size. Your calibration is remembered in your browser, and everything runs locally, so nothing about your device is sent anywhere.
Esc to exit. Double-click or hit Clear to remove a measurement.A screen ruler is the thing you didn't know you'd reach for until you need it:
Browsers don't tell a web page the true physical size of your screen, only its pixel resolution, so the ruler starts from a common assumption of about 96 pixels per inch. That's close on many laptops but off on phones and high-density displays. One quick calibration with a bank card fixes it exactly, and we remember the setting for next time.
Every credit, debit, and ID card follows the ISO/IEC 7810 ID-1 standard, which makes them all exactly 85.6 mm (about 3.37 inches) wide. By matching the on-screen box to a real card, you're telling the ruler precisely how many pixels equal one inch on your display — the one number it needs to be accurate.
Click and drag along the ruler from one end of the object to the other. The shaded band marks your span and the exact length appears above the ruler. If you just want the distance from the start of the ruler, hover without clicking and read the live value at the pointer.
For most modern screens, gently resting a card or a smooth object is fine — phone glass in particular is tough. Take care with anything metal, sharp, or gritty that could scratch the surface, and never press hard. Rest the object lightly rather than pushing it into the display.
Yes. Touch works just like the mouse — drag a finger along the ruler to measure a span. On a phone, switching to the vertical orientation usually gives you the most measuring length to work with.
Completely. The ruler runs entirely in your browser, your calibration is stored only on your own device, and nothing is uploaded or logged. It keeps working offline once the page has loaded.