Practical tools for measured work
Calibrated screen ruler
Measure screen-plane lengths after physical calibration, with millimetre or sixteenth-inch ticks and zoom/resize invalidation.
Place a physical ruler or an object of measured length against the screen. Adjust the blue bar until its two ends match that known length, then confirm calibration. Browser pixels alone do not establish real size.
Calibration required. Recalibrate after changing zoom, window size, screen or orientation.
Limitations
Calibration is local to this browser window and is not saved. Moving to another display requires recalibration even if the browser reports no change. Check a second known length before using the ruler. This measures screen-plane lengths, not an object photographed at an unknown scale.
Related tools
How to read a ruler
Select ruler ticks and see reduced inch fractions, decimal inches and millimetres in an interactive reading guide.
Printable Ruler
Prepare a full-size metric, imperial or combination ruler and verify the printed calibration square before use.
Printable Protractor
Prepare a full-size 180° protractor and verify its printed calibration mark before use.
Graph Paper
Create calibrated square or dot-grid paper, draw on it locally, and export a single-sheet PDF or SVG image.