Manually calibrated screen ruler
Match a reference of 1 to 1000 mm with 20 to 2000 CSS px, then calibrate (ratio up to 40 px/mm).
- Runs in your browser
- No upload
- Check the displayed result
Inputs stay in this tab and are not uploaded or saved automatically. Optional aggregate usage counts and coarse processing diagnostics are sent only after consent, without input content or filenames. Clearing or closing loses inputs; save needed outputs first.
Method and limits
Match a reference of 1 to 1000 mm with 20 to 2000 CSS px, then calibrate (ratio up to 40 px/mm). The length can be 10 to 250 mm. The ruler is UNKNOWN before calibration. Resizing, zooming, a change of device pixel ratio, moving to another screen or hiding the tab invalidates it, and monitor changes the browser can't detect need a manual recalibration. Print the SVG at 100% and check a known physical measure separately. This is a local browser observation only: no hardware diagnosis and no universal accuracy. Nothing is stored, recorded or uploaded, and no private-data telemetry is sent. Stop or reset clears the session. Browser, OS or permissions may leave results UNKNOWN.
UNKNOWN / not observed
How to use
- Start
Line up a known physical reference with the screen guide. Enter its length in millimeters and the span you measured in CSS pixels, then calibrate. Before calibration, the scale is UNKNOWN.
- Stop / Reset
A 50 mm reference spanning 200 CSS px gives 4 CSS px/mm. A 10 mm segment then spans 40 CSS px under the same conditions.
- Download result
Check the alignment again on the same screen. Zoom, orientation or screen changes can invalidate the calibration, so recalibrate before you measure again.
Questions and limits
What does this result mean?
CSS pixels are layout units, not a fixed hardware length. Manual calibration supplies the physical scale for this particular viewing setup.
How do I resolve rejected or missing input?
Use a reference of 1…1000 mm and a span of 20…2000 CSS px within the permitted ratio. Correct rejected values instead of assuming the display’s nominal DPI.
What are the limits of this tool?
No guarantee of hardware accuracy. The downloadable millimeter SVG is a separate print ruler: print at 100% and check it against a known reference physically.