What is an aspect ratio?
The aspect ratio of a picture, a screen or a video is the relationship between its width and its height, written as width:height. A 1920 x 1080 picture has an aspect ratio of 16:9, because dividing both numbers by 120 gives 16 and 9. The ratio stays the same at any size, so 1280 x 720 and 3840 x 2160 are also 16:9. It describes the shape, not the number of pixels.
How to calculate the aspect ratio
- Divide the width and the height by their greatest common divisor, the largest number that divides both exactly.
- Write the results as width:height.
For 1920 x 1080, the greatest common divisor is 120. 1920 / 120 = 16 and 1080 / 120 = 9, so the ratio is 16:9. You can also divide the width by the height to get a decimal ratio: 1920 / 1080 = 1.78, written 1.78:1.
Some sizes do not reduce to small numbers. 1366 x 768 reduces to 683:384, which is very close to 16:9. In that case the calculator also shows the closest common ratio.
How to resize and keep the aspect ratio
To keep the shape when you change one side, scale the other side by the same amount.
new height = new width x original height / original width
new width = new height x original width / original heightA 1920 x 1080 picture resized to a width of 1280 has a height of 1280 x 1080 / 1920 = 720. Fill in either the new width or the new height, and the calculator works out the other.
Round to even numbers for video
Many video encoders need a width and a height that are even numbers, and some work best with multiples of 4, 8 or 16. A width of 1001 on a 16:9 video gives a height of 563.06, which has to be rounded. Choose Round to a multiple of 2 and the calculator rounds to the nearest even size. The result is not exactly the same ratio, and the calculator tells you how far off it is.
Common aspect ratios
| Ratio | Decimal | Typical use |
|---|---|---|
| 1:1 | 1.00 | Social media posts, profile pictures, product photos |
| 5:4 | 1.25 | 8 x 10 inch prints, some older monitors |
| 4:3 | 1.33 | Older TVs and monitors, many tablets, many compact cameras |
| 3:2 | 1.50 | 35 mm film, most DSLR and mirrorless cameras, 4 x 6 inch prints |
| 16:10 | 1.60 | Some laptops and monitors |
| 16:9 | 1.78 | HD and 4K video, YouTube, most TVs and monitors |
| 2:1 | 2.00 | Wide banners and some films |
| 21:9 | 2.33 | Ultrawide monitors (real sizes are about 2.37:1) and some films |
| 4:5 | 0.80 | Portrait posts on Instagram |
| 9:16 | 0.56 | Vertical video: Stories, Reels, Shorts, TikTok |
Popular resolutions and their aspect ratios
| Resolution | Aspect ratio | Name |
|---|---|---|
| 1920 x 1080 | 16:9 | Full HD, 1080p |
| 1280 x 720 | 16:9 | HD, 720p |
| 3840 x 2160 | 16:9 | 4K UHD |
| 2560 x 1440 | 16:9 | QHD, 1440p |
| 1366 x 768 | 683:384, about 16:9 | Common laptop screen |
| 1920 x 1200 | 16:10 | WUXGA |
| 1440 x 900 | 16:10 | WXGA+ |
| 1024 x 768 | 4:3 | XGA |
| 2048 x 1536 | 4:3 | QXGA |
| 1080 x 1080 | 1:1 | Square post |
| 1080 x 1350 | 4:5 | Instagram portrait post |
| 1080 x 1920 | 9:16 | Vertical video |
| 2560 x 1080 | 64:27, about 21:9 | Ultrawide |
| 3440 x 1440 | 43:18, about 21:9 | Ultrawide |
| 4096 x 2160 | 256:135, about 1.9:1 | DCI 4K cinema |
Ratio pages and other tools
For a particular shape, use the 16:9, 4:3 or 1:1 calculator, with sizes and the crop needed to reach that ratio. To scale from a ratio, or fit a picture inside a box, use the width and height calculator. To change a picture, crop it to a ratio or resize it. The aspect ratio guide explains how to change a ratio without distortion, and has CSS and video commands. To work out percentages of a size, use the percentage calculator.