Screen Size Calculator

A screen's advertised size is its diagonal, which says little on its own: a 34-inch ultrawide is barely taller than a 27-inch 16:9 monitor. This calculator turns a diagonal and aspect ratio into the real width, height and area in inches and centimetres, works out pixel density when you enter a resolution, and compares two screens so you can see which is wider, taller or larger before you buy.

How to use this tool

1. Enter the diagonal in inches or centimetres.
2. Pick the aspect ratio — or enter the resolution, whose own ratio is then used and which also gives pixels per inch.
3. Tick "Compare" and describe a second screen to see the differences.
4. Read the width, height, area and ratios.

Formula

width = d × a ÷ √(a² + b²) · height = d × b ÷ √(a² + b²) · PPI = √(px_w² + px_h²) ÷ d

d is the diagonal and a:b the aspect ratio. "21:9" ultrawides are not exactly 21:9: 3440 × 1440 panels are 43:18 (2.39:1) and 2560 × 1080 panels 64:27 (2.37:1), so both are listed separately.

Example

A 27-inch 16:9 monitor is 27 × 16 ÷ √337 = 23.53 in wide and 13.24 in tall (59.8 × 33.6 cm); at 2560 × 1440 that is 108.8 PPI. A 34-inch 3440 × 1440 ultrawide is 31.36 × 13.13 in: about 32% more area but 0.8% less height than the 27-inch screen.