acalculator

What are my screen size dimensions?

Screens are sold by their diagonal. Type the diagonal size and pick the aspect ratio to see how wide and tall the picture really is, and its area, in inches or centimeters.

Your numbers

Units
Aspect ratio
Width
23.53 in

A 27 in screen at 16:9 is 23.53 in wide and 13.24 in tall.

Height
13.24 in
Screen area
311.5 in²
Ratio
1.778:1

Width: 23.53 in. A 27 in screen at 16:9 is 23.53 in wide and 13.24 in tall.

How to calculate

Works out the width, height and area of a TV, monitor or phone screen from its diagonal size and aspect ratio, such as 16:9, 21:9 or 4:3.

Example with the default inputs (Diagonal size 27 in, Aspect ratio 16:9): A 27 in screen at 16:9 is 23.53 in wide and 13.24 in tall.

Method: For an aspect ratio a : b and diagonal d: width = d × a ÷ √(a² + b²); height = d × b ÷ √(a² + b²).

  • The diagonal is the visible picture, corner to corner, as screen sizes are sold.
  • A 21:9 screen is taken as exactly 21:9; real ultrawides are close to it (2560 × 1080 is 64:27, 2.37:1).

Machine-readable copies: Markdown, JSON.

Worked examples

Each example is checked against the calculator on every build.

  1. Diagonal size 27 in, Aspect ratio 16:9 gives Width 23.53 in, Height 13.24 in, Screen area 311.5 in², Ratio 1.778:1.Source: OpenStax, Prealgebra 2e, §9.3 Use Properties of Angles, Triangles, and the Pythagorean Theorem (a² + b² = c²), https://openstax.org/books/prealgebra-2e/pages/9-3-use-properties-of-angles-triangles-and-the-pythagorean-theorem (retrieved 2026-10-03)
  2. Diagonal size 20 in, Aspect ratio 4:3 gives Width 16 in, Height 12 in, Screen area 192 in², Ratio 1.333:1.Source: OpenStax, Prealgebra 2e, §9.3 Use Properties of Angles, Triangles, and the Pythagorean Theorem (a² + b² = c²), https://openstax.org/books/prealgebra-2e/pages/9-3-use-properties-of-angles-triangles-and-the-pythagorean-theorem (retrieved 2026-10-03)
  3. Diagonal size 33.86 in, Aspect ratio Other, Width 32, Height 9 gives Width 32.59 in, Height 9.17 in, Ratio 3.556:1.Source: OpenStax, Prealgebra 2e, §9.3 Use Properties of Angles, Triangles, and the Pythagorean Theorem (a² + b² = c²), https://openstax.org/books/prealgebra-2e/pages/9-3-use-properties-of-angles-triangles-and-the-pythagorean-theorem (retrieved 2026-10-03)

How it works

The width, height and diagonal of a screen form a right triangle, so width² + height² = diagonal² (Pythagoras). For an aspect ratio a : b and a diagonal d:

  • width = d × a ÷ √(a² + b²)
  • height = d × b ÷ √(a² + b²)
  • area = width × height
  • ratio = a ÷ b, shown as x : 1 with 4 significant figures.

The listed ratios are 16:9, 16:10, 21:9, 4:3 and 2.39:1, each taken exactly as written. With Other you type the two parts (from 0.01 to 1,000), for example 32 and 9, or a screen's pixels such as 3440 and 1440.

Rules

  • The diagonal is 0.1 in to 2,000 in, typed in inches or centimeters, and used as the exact decimal typed.
  • Results show in inches in US units and centimeters in Metric.

Worked examples by hand

27 in at 16:9. √(16² + 9²) = √337 = 18.358. Width 27 × 16 ÷ 18.358 = 23.53 in; height 27 × 9 ÷ 18.358 = 13.24 in; area 311.5 in²; ratio 1.778:1.

20 in at 4:3. √(4² + 3²) = 5. Width 20 × 4 ÷ 5 = 16 in; height 20 × 3 ÷ 5 = 12 in; area 192 in².

86 cm at 32:9. √(32² + 9²) = √1105 = 33.242. Width 86 × 32 ÷ 33.242 = 82.79 cm; height 86 × 9 ÷ 33.242 = 23.28 cm; ratio 3.556:1.

Other questions people ask

How do I find the width and height of a screen from its diagonal?

For an aspect ratio a : b, the diagonal of a screen a wide and b tall is √(a² + b²). Scale it to your diagonal: width = diagonal × a ÷ √(a² + b²), and height = diagonal × b ÷ √(a² + b²).

How wide is a 65 inch TV?

A 65 in 16:9 TV is 65 × 16 ÷ 18.36 = 56.7 in wide and 31.9 in tall (the picture only; the frame adds a little).

Why is a 21:9 monitor smaller than a 16:9 monitor of the same size?

At the same diagonal, a wider ratio gives a shorter and smaller screen. A 34 in 21:9 monitor is about 31.3 in by 13.4 in, about the height of a 27 in 16:9 monitor.

Does the screen size include the bezel?

No. The size a screen is sold by is the diagonal of the visible picture. Measure the case to know the outside size.

Is a 34 inch ultrawide really 21:9?

Nearly. 2560 × 1080 is 64:27 (2.37:1) and 3440 × 1440 is 43:18 (2.39:1), both sold as 21:9 (2.33:1). Pick Other and type the pixels as the ratio for an exact answer.