Screen Size Calculator
Turn a screen’s diagonal and aspect ratio into its real width and height in inches and centimetres, plus the display area.
How it works
Width = diagonal × w ÷ √(w² + h²) · Height = diagonal × h ÷ √(w² + h²)
A screen is measured corner to corner, but its width and height depend on the aspect ratio. Treating the ratio as the sides of a right triangle, the diagonal is √(w² + h²) in ratio units, so scaling the diagonal by w or h over that length recovers each dimension. This is why a 27-inch 16:9 monitor and a 27-inch 4:3 monitor have very different widths — and areas.
Worked example
A 27-inch 16:9 screen: √(16² + 9²) = √337 ≈ 18.36. Width = 27 × 16 ÷ 18.36 = 23.53 in; height = 27 × 9 ÷ 18.36 = 13.24 in. Area = 23.53 × 13.24 ≈ 311.5 sq in.
Frequently asked questions
Why do two screens with the same diagonal look different sizes?
Because the diagonal splits between width and height according to the aspect ratio. A wide 21:9 monitor and a square-ish 4:3 one with the same diagonal have very different widths, heights and total areas — a 16:9 screen actually has less area than a 4:3 screen of the same diagonal.
How do I find the display area?
Multiply the calculated width by the height. This tool shows the area in both square inches and square centimetres, which is the fair way to compare how much you actually see across different aspect ratios.
What aspect ratio should I enter?
Use 16:9 for most TVs and monitors, 21:9 for ultrawide, 16:10 for many laptops, 4:3 for older displays, and 3:2 for some tablets and laptops. Enter the two numbers as the ratio width and height.
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This calculator is for educational purposes. Double-check important results before acting on them.