Screen Size Test — What is My Screen Size in Inches?
Calibrate physical screen dimensions against a standard reference card to calculate true display diagonal inches and width/height span.
Calibrate Scale to Estimate Physical Screen Size
Hold a standard credit card (85.60 mm wide) against your screen. Adjust the slider below until the card box on screen matches your real physical card.
Physical Dimensions vs CSS Pixels
Because a 14-inch laptop and a 27-inch desktop monitor can both share a 2560×1440 resolution, pixel count alone cannot reveal physical display diagonal. Manual standard-object calibration establishes the bridge between on-screen pixels and real-world physical millimeters.
Frequently Asked Questions
Can web browsers automatically detect the physical inch size of my monitor?
No. Web browsers only have access to CSS pixel counts and operating system scaling ratios. Physical dimensions (such as 27 inches or 32 inches) are not exposed by standard browser APIs.
How does the credit-card calibration tool work?
Standard ISO/IEC 7810 ID-1 credit cards have a globally standardized physical width of exactly 85.60 mm (3.37 inches). By aligning an on-screen reference box with a physical card held against the screen, the tool calculates your true physical pixel density and determines your exact monitor diagonal in inches.
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