Actual Size Ruler for Real-World Measurements

A screen ruler becomes meaningful in real physical units only after the display scale is known. Calibrate the screen, keep the scale unchanged and use the ruler as a quick real-size reference.

Calibration is stored only in this browser.
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Drag across the ruler to measure a span.
⌨ Keyboard shortcuts

C cm · I inch · P px · R rotate · F fullscreen · G guides · X crosshair · A angle · D dark · 4 four edges

Calibrate1Ruler

Match a standard bank card width (85.60 mm) to the guide below.

85.60 mm

What “actual size” means on a screen

Actual size means that a centimeter drawn by the browser occupies one physical centimeter on the display, and the same principle applies to inches. This cannot be assumed from resolution alone because screens with identical pixel counts can have different physical dimensions.

Two practical calibration methods

The bank-card method directly matches the display to a known 85.60 mm width. The diagonal method uses the active screen’s stated physical diagonal together with the browser-reported screen dimensions. The card method is usually easier when the exact monitor model is unknown.

Keep the calibration tied to one display

If you move the browser window to a second monitor, change display scaling or alter browser zoom, recalibrate before relying on real-size measurements. The saved value is a convenience, not a universal setting for every screen.

Use actual-size mode for quick checks, not certification

The tool is suited to small everyday comparisons and planning. Precision manufacturing, medical fitting, legal measurement and other critical work require an appropriate physical instrument.