screendimensions.com

Screen Dimensions is a free web page that reads the dimensions, display resolution, pixel ratio, browser window size, refresh rate and color range of the screen you are using. The readings appear in your browser as soon as the page opens, and the site states that nothing about your screen is sent to a server.

Browsers cannot report physical size, so the site offers a way to estimate it. You hold any bank card against the screen and match it on the display, since a standard card is 85.6 mm wide, and the site works out the diagonal in inches. The site also explains how to find a screen's size from its model name on a Windows PC, Mac, iPhone, Android phone or TV, and includes a dead pixel test, a refresh rate test and a touch screen test.

The site is a reference for anyone choosing or checking a TV, monitor, laptop or phone. It includes charts of width and height for common screen sizes, aspect ratio formulas, pixel counts for common resolutions such as 1080p and 4K, and comparison tools for screen sizes and iPhone models drawn to scale.