# What are my screen size dimensions?

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.

- Page: https://www.acalculator.org/everyday-life/screen-size-calculator
- JSON spec: https://www.acalculator.org/everyday-life/screen-size-calculator.json
- Version: 2bd6ff2a317a

## Default answer

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.

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| d | Diagonal size | The screen size, measured corner to corner across the visible picture. |
| ar | Aspect ratio | Width to height: 16:9 for TVs and most monitors, 16:10 for many laptops, 21:9 ultrawide. |
| rw | Width | The width part of the ratio, for example 32 in 32:9. |
| rh | Height | The height part of the ratio, for example 32 in 32:9. |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| width | Width | Diagonal × a ÷ √(a² + b²) for a ratio a : b. |
| height | Height | Diagonal × b ÷ √(a² + b²). |
| area | Screen area | Width × height. |
| ratio | Ratio | Width ÷ height, as x : 1. |

## Method

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

## Assumptions

- 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).

## Worked examples

1. d = 0.6858, ar = 16:9 gives width = 0.597727, height = 0.336221, area = 0.200968, 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. d = 0.508, ar = 4:3 gives width = 0.4064, height = 0.3048, area = 0.123871, 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. d = 0.86, ar = custom, rw = 32, rh = 9 gives width = 0.82788, height = 0.232841, 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).

## FAQ

### 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.

## Sources

- OpenStax, Prealgebra 2e, §9.3 Use Properties of Angles, Triangles, and the Pythagorean Theorem (a² + b² = c² for a right triangle). https://openstax.org/books/prealgebra-2e/pages/9-3-use-properties-of-angles-triangles-and-the-pythagorean-theorem (retrieved 2026-10-03)