Online Ruler

CSS pixels do not always match the physical size of your display

Browsers draw interfaces in CSS pixels. Their relationship with real millimeters depends on density, zoom and system scaling. This ruler therefore offers manual PPI adjustment for approximate measurement.

Adjust the scale before measuring

1. Choose centimeters or inches depending on your measurement.
2. Use an 85.6 mm card as reference and tune PPI until the width matches.
3. After calibration, carefully place the object near the screen and use the visual scale.

Sources and references for this tool

These references help contextualize formulas, standards, APIs and limitations used on this page. They do not replace professional validation when a result has legal, financial, medical or operational impact.

• CSS Values and Units Module Level 4W3C — Definitions of CSS units and their relationship with visual media.
• CSSOM View ModuleW3C — Context for viewport and layout measurements in the browser.

Frequently asked questions

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