How to calculate an aspect ratio
Divide the width and the height by their greatest common divisor. For 1920 × 1080 that's 120, so the ratio is 1920 ÷ 120 : 1080 ÷ 120 = 16:9. For 1080 × 1350 it's 270, which gives 4:5.
The calculator does this as you type and also shows the decimal form (16:9 is 1.78:1), the megapixel count and the orientation. To check a photo you already have, use Read from an image: it reads the pixel size in your browser without uploading anything.
How to find the height (or width) for a ratio
Multiply the side you know by the other side of the ratio, then divide by its own side:
- Height = width × ratio height ÷ ratio width. At 4:5, a 1080 px wide image is 1080 × 5 ÷ 4 = 1350 px tall.
- Width = height × ratio width ÷ ratio height. At 16:9, a 720 px tall image is 720 × 16 ÷ 9 = 1280 px wide.
Pick the ratio on the right, type either side, and the other fills in. The swap button turns a landscape ratio into its portrait twin (16:9 into 9:16).
Common aspect ratios
| Ratio | Decimal | Typical use | Common sizes |
|---|---|---|---|
| 1:1 | 1.00 | Square posts, profile pictures | 1080 × 1080 |
| 4:5 | 0.80 | Instagram and Facebook portrait posts | 1080 × 1350 |
| 3:4 | 0.75 | Instagram grid, phone photos held upright | 1080 × 1440 |
| 2:3 | 0.67 | Pinterest pins, 4 × 6 prints | 1000 × 1500 |
| 9:16 | 0.56 | Stories, Reels, TikTok, Shorts | 1080 × 1920 |
| 4:3 | 1.33 | Phone photos, iPad, older TVs | 1600 × 1200 |
| 3:2 | 1.50 | DSLR and mirrorless photos | 3000 × 2000 |
| 16:9 | 1.78 | Video, YouTube, TVs, slides | 1920 × 1080 |
| 16:10 | 1.60 | Laptop screens | 1920 × 1200 |
| 21:9 | 2.33 | Ultrawide monitors, cinema | 2560 × 1080 |
| 1.91:1 | 1.91 | Link previews, landscape feed posts | 1200 × 628 |
Platform-by-platform sizes are on the social media image sizes cheat sheet.
When the ratio doesn't come out clean
Plenty of real sizes don't reduce to small numbers. 1366 × 768, a common laptop resolution, is exactly 683:384, which is within 0.1% of 16:9. A Facebook cover at 851 × 315 is 2.7:1. When the exact ratio is ugly, the calculator shows the decimal form and the nearest standard ratio, with how far off it is. Under about 1%, the difference is a few pixels and nobody will notice. At 3% or more you'll see bars or a crop.
21:9 is a marketing name, too: 2560 × 1080 is really 64:27 (2.37:1) and 3440 × 1440 is 43:18 (2.39:1).
Aspect ratio vs resolution
The ratio is the shape; the resolution is how many pixels fill it. 1280 × 720, 1920 × 1080 and 3840 × 2160 are all 16:9. Scaling an image up or down keeps its ratio. Changing the ratio means changing what's in the picture: cropping something away or adding space.
How to change an image's aspect ratio
- Crop. The 4:3, 16:9 and 1:1 croppers, or the crop tool with any custom ratio, let you choose what to keep.
- Fit with padding. The size pages' Fit whole image option keeps the whole picture and fills the gap with a blur or a solid color.
- Don't stretch. Forcing a 4:3 photo into 16:9 without cropping or padding makes people look a third wider.
Every tool runs in your browser, so the image never leaves your device.
