What aspect ratio is
The aspect ratio is the proportion of width to height, written like 4:3 or 16:9. A photo that is 4,000 by 3,000 pixels has a ratio of 4:3. If you change only the width, or you scale both sides by the same factor, the ratio stays the same. If you change them by different factors, the picture is stretched.
new height = new width x (original height / original width) 4,000 x 3,000 resized to a width of 1,200: 1,200 x (3,000 / 4,000) = 900 => 1,200 x 900
How this page keeps the ratio
Enter the width, the height, or both, and the setting Fit inside is used. With one value, the other is calculated. With both, the picture is scaled to fit within that box and keeps its shape, so one of the sides can end up shorter than the box.
Common aspect ratios and sizes
| Ratio | Example size | Common use |
|---|---|---|
| 1:1 | 1,080 x 1,080 | Square posts, profile pictures |
| 4:5 | 1,080 x 1,350 | Portrait posts |
| 3:2 | 1,500 x 1,000 | Camera photos, prints |
| 4:3 | 1,600 x 1,200 | Phones, older screens, product photos |
| 16:9 | 1,920 x 1,080 | Video, thumbnails, slides |
| 9:16 | 1,080 x 1,920 | Stories, Reels, Shorts |
| 2:3 | 1,000 x 1,500 | Portrait prints, Pinterest |
When you need a different ratio
To get a new shape without stretching, you have to cut or pad. Choose Fill and crop to cut the edges evenly, or Fit with padding to add a colour border. Both give you the exact size. Social media and passport sizes work this way: see Instagram and passport photo.
Mistakes to avoid
- Typing both sides with different ratios and choosing Stretch.
- Resizing in a web page with CSS width and height that do not match, which squashes the image on screen. Set one side and let the other be
auto. - Rounding errors. Whole pixels are needed, so 1,200 x 900.4 becomes 1,200 x 900.
Other presets: Percentage. The guide to resizing images covers more.