How to calculate an aspect ratio
An aspect ratio is the proportion between width and height. To find it, divide both numbers by their greatest common divisor. For 1920 × 1080 that divisor is 120, which gives 16:9. For 1080 × 1350 it is 270, which gives 4:5. The decimal form divides width by height: 16:9 is about 1.78:1.
Find a missing width or height
With a ratio of W:H, height = width × H ÷ W and width = height × W ÷ H. A 16:9 video 1280 pixels wide is 720 pixels high; a 9:16 vertical video 1920 pixels high is 1080 pixels wide. Rounding to whole pixels can move the result very slightly off the exact ratio, which is normal.
| Ratio | Decimal | Example size | Used for |
|---|---|---|---|
| 16:9 | 1.78 | 1920 × 1080 | YouTube, TV, most monitors |
| 9:16 | 0.56 | 1080 × 1920 | Shorts, Reels, TikTok, Stories |
| 4:3 | 1.33 | 1024 × 768 | Older screens, iPad, many phone photos |
| 3:2 | 1.5 | 1800 × 1200 | DSLR photos, 4×6 prints |
| 4:5 | 0.8 | 1080 × 1350 | Portrait social feed posts, 8×10 prints |
| 1:1 | 1 | 1080 × 1080 | Square posts, profile pictures |
| 21:9 | 2.33 | 2560 × 1080 (64:27) | Ultrawide monitors, cinematic video |
Changing an image’s ratio
Resizing keeps the ratio only when width and height change by the same factor. To change the ratio itself, for example a 4:3 photo to 16:9, you must crop or add borders; stretching distorts faces and objects. Once the ratio is right, set the exact pixels with the Image Resizer. For platform-by-platform video sizes, see video aspect ratios and sizes; for prints, the 4×6 and 5×7 photo size guides explain cropping.
Frequently asked questions
How do I calculate an aspect ratio?
Divide the width and 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. Enter any width and height above to get the result instantly.
How do I find the height for a 16:9 width?
Multiply the width by 9 and divide by 16. A 1280-pixel-wide 16:9 image is 1280 × 9 ÷ 16 = 720 pixels high. For the width from a height, multiply the height by 16 and divide by 9.
What aspect ratio is 1080 × 1350?
4:5. Both numbers divide by 270, giving 4 × 5. It is the tall portrait format used for many social media feed posts.
Is 2560 × 1080 really 21:9?
Not exactly. 2560 × 1080 reduces to 64:27, about 2.37:1, while 21:9 is 2.33:1. Monitors and phones with roughly that shape are marketed as 21:9, so the calculator shows both.