About us
About Online Display Ruler
A free browser-based screen ruler for quick reference measurements, with calibration controls for physical units.
Online Display Ruler helps when you need a quick scale beside your browser workspace. It is useful for checking small, flat objects, comparing lengths, or making a screen layout reference without installing an app or creating an account. The ruler is rendered in the page and works as part of this statically generated Astro website.
Tools and units
The ruler supports centimeters, millimeters, inches, and CSS pixels. Inch mode can display fractional or decimal marks. Choose which workspace corners and edges show the scale, use a guide to mark an alignment, or select two points to read a distance. A crosshair can show cursor coordinates, and readings can be copied. The interface also provides keyboard controls, fullscreen mode, and light and dark themes.
Calibration and screen size
A browser knows CSS pixels, but does not know the verified physical dimensions of the display. For actual-size physical measurements, calibrate the scale against the on-screen outline of a standard ID-1 card (85.60 × 53.98 mm). A screen diagonal can also produce an estimate, but it depends on reported dimensions and is less direct. Keep browser zoom at 100% while calibrating and repeat calibration after changing screens, zoom, or operating-system display scaling.
Even after calibration, placement, viewing angle, display behavior, and the reference object can affect results. This is a convenience tool for everyday checks, not certified measuring equipment. Do not rely on it for medical, safety-critical, or engineering-tolerance decisions.
Usability and feedback
The site keeps the ruler available directly in the browser and uses the same page for mouse and keyboard measurement. Calibration and theme choices are stored locally in the browser. Google Analytics runs on production pages to measure page traffic; the site does not send custom ruler-reading events, serve ads, or measure objects through a camera.
For a bug report, calibration question, feature suggestion, or accessibility issue, visit Contact Us. You can also open the ruler or read the measurement and calibration guide.