# What is my aspect ratio?

Finds the aspect ratio of a width and height in lowest terms (1920 × 1080 is 16:9) with the closest common ratio, or resizes to a ratio from a new width or height.

- Page: https://www.acalculator.org/math/aspect-ratio-calculator
- JSON spec: https://www.acalculator.org/math/aspect-ratio-calculator.json
- Version: 490832a00953

## Default answer

Example with the default inputs (I want to Find the ratio, Width 1,920, Height 1,080): A size of 1,920 × 1,080 has an aspect ratio of 16:9.

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| mode | I want to | Find the ratio of a size, or resize to a ratio from a new width or a new height. |
| w | Width | The width of the screen, image, or video, in pixels or any unit. |
| h | Height | The height, in the same unit as the width. |
| rw | Ratio width | The first number of the ratio W:H, such as 16 in 16:9. |
| rh | Ratio height | The second number of the ratio W:H, such as 9 in 16:9. |
| nw | New width | The width you want; the height is found from the ratio. |
| nh | New height | The height you want; the width is found from the ratio. |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| ratio | Aspect ratio | Width : height in lowest whole-number terms. |
| width | Width | The width of the size. |
| height | Height | The height of the size. |
| decimal | Ratio as a decimal | Width ÷ height, the ratio written as x:1. |
| common | Closest common ratio | The common aspect ratio nearest to this one, such as 16:9 or 4:3. |

## Method

Aspect ratio = width : height, divided by their greatest common divisor; a new height is new width × H ÷ W (and a new width is new height × W ÷ H).

## Assumptions

- Width and height are positive numbers in one unit, usually pixels; decimals are read exactly (2.39 is 239/100).
- Resizing keeps the ratio exactly, so a solved side may not be a whole number of pixels.
- The closest common ratio is the nearest of 1:1, 5:4, 4:3, 3:2, 16:10, 16:9, 1.85:1, 2:1, 21:9, and 2.39:1, flipped for a portrait size.

## Worked examples

1. mode = ratio, w = 1,920, h = 1,080 gives ratio = 16:9, decimal = 1.777778, common = 16:9. Source: ITU-R Recommendation BT.709-6, 1920 × 1080 at 16:9 (https://www.itu.int/rec/R-REC-BT.709).
2. mode = ratio, w = 1,366, h = 768 gives ratio = 683:384, decimal = 1.778646, common = 16:9.
3. mode = ratio, w = 1,080, h = 1,920 gives ratio = 9:16, common = 9:16.
4. mode = width, rw = 16, rh = 9, nw = 1,280 gives height = 720, width = 1,280, ratio = 16:9.
5. mode = height, rw = 4, rh = 3, nh = 1,000 gives width = 1,333.333333, ratio = 4:3.
6. mode = ratio, w = 2.39, h = 1 gives ratio = 239:100, decimal = 2.39, common = 2.39:1.

## FAQ

### How do I calculate an aspect ratio?

Divide the width and the height by their greatest common divisor. For 1920 × 1080, the greatest common divisor is 120, so the ratio is 1920 ÷ 120 : 1080 ÷ 120 = 16:9.

### How do I find the height for a width at 16:9?

Multiply the width by 9 and divide by 16. A 1280-pixel-wide video at 16:9 is 1280 × 9 ÷ 16 = 720 pixels high. For the width from a height, multiply by 16 and divide by 9.

### Why is my screen not exactly 16:9?

Some sizes are rounded to whole pixels or to what the panel maker could build. A 1366 × 768 laptop screen is 683:384 exactly, which is 1.7786:1, very close to 16:9 (1.7778:1). The calculator shows 16:9 as the closest common ratio.

### What are the common aspect ratios?

16:9 for HD and 4K video and most TVs and monitors; 4:3 for older TVs, iPads, and many cameras; 3:2 for 35 mm photos; 16:10 for some laptops; 1:1 for square posts; 9:16 for phone videos held upright; 1.85:1 and 2.39:1 for cinema; 21:9 (really 64:27, about 2.37:1) for ultrawide monitors such as 2560 × 1080. A 3440 × 1440 monitor, sold as 21:9, is 43:18, closer to 2.39:1.

### What does an aspect ratio of 2.39:1 mean?

The width is 2.39 times the height. Written with whole numbers it is 239:100. The calculator reads decimals exactly, so a width of 2.39 and a height of 1 give 239:100.

### Why is my resized height not a whole number?

The calculator keeps the ratio exactly. 1000 pixels high at 4:3 needs a width of 1333.33 pixels; round it to a whole pixel yourself (1333 or 1334), which changes the ratio very slightly.

### Does the order of width and height matter?

Yes. Aspect ratios are written width first. A phone video held upright is 1080 × 1920, which is 9:16, the portrait form of 16:9.

## Sources

- SMPTE ST 2036-1:2014, Ultra High Definition Television: Image Parameter Values for Program Production (16:9 aspect ratio, 3840 × 2160 and 7680 × 4320).
- ITU-R Recommendation BT.709-6 (2015), Parameter values for the HDTV standards (16:9, 1920 × 1080). https://www.itu.int/rec/R-REC-BT.709
- OpenStax, Prealgebra 2e, §6.5 Solve Proportions and their Applications (equal ratios, cross products). https://openstax.org/books/prealgebra-2e/pages/6-5-solve-proportions-and-their-applications