Display Calculators
Screen width and height from the diagonal.
Enter the diagonal and the aspect ratio to get the screen width, height and area in inches and centimetres, a table of common TV sizes, and the largest diagonal that fits a given width such as a stand or alcove. The panel only; the bezel and stand add to it. Runs in your browser; nothing is sent or stored.
Inputs
Result
Fill the form and press Calculate.
Worked example
A 55 inch 16:9 screen: the ratio diagonal is sqrt(16^2 + 9^2) = 18.36, so each unit of the ratio is 55 / 18.36 in. Width = 16 x 55 / 18.36 = 47.9 in (121.8 cm) and height = 9 x 55 / 18.36 = 27.0 in (68.5 cm). A stand that is 48 in wide fits a diagonal of up to 48 x 18.36 / 16 = 55.1 in at 16:9.
How it works
With aspect ratio a:b, width = diagonal x a / sqrt(a^2 + b^2) and height = diagonal x b / sqrt(a^2 + b^2) (Pythagorean theorem). Multiply inches by 2.54 for centimetres. Check the product spec for the bezel and stand.
Ratios are nominal. As the Ultrawide formats - Wikipedia article explains, 21:9 is a marketing term for ratios such as 64:27 and 43:18 (3440 x 1440), so pick 43:18 for a 3440 x 1440 monitor.
Sources: Ultrawide formats - Wikipedia. Each opened 2026-10-08.
Planning guide only, not professional advice. Figures are estimates from the inputs you enter.
FAQ
How do I find screen width from the diagonal?
Multiply the diagonal by a and divide by sqrt(a^2 + b^2) for an a:b screen. For a 16:9 screen the width is the diagonal x 0.8716. A 55 inch screen is 47.9 in wide.
What are the dimensions of a 55 inch TV?
The 16:9 panel is about 47.9 in wide and 27.0 in tall (121.8 x 68.5 cm), before the bezel and stand.
Does the stand add to the width?
It can. This calculator gives the panel, so check the product spec sheet for the full width and for the stand footprint before buying furniture.
Why is my 21:9 monitor not exactly 21:9?
Because 21:9 is a marketing term. Real panels are commonly 64:27 or 43:18, and the 43:18 option matches a 3440 x 1440 monitor.