Aspect ratio explained: how to calculate and keep it
Updated 21 October 2026
Tool for this guide: Aspect ratio calculator
Short answer: aspect ratio is the shape of an image or screen, written as width:height. Divide both numbers by their greatest common divisor: 1920 × 1080 becomes 16:9. The aspect ratio calculator does this and fills in the missing width or height when you resize.
Common aspect ratios
| Ratio | Example size | Used for |
|---|---|---|
| 16:9 | 1920 × 1080 | HD and 4K video, YouTube, monitors, TVs |
| 9:16 | 1080 × 1920 | Stories, Reels, TikTok, Shorts |
| 1:1 | 1080 × 1080 | Square posts, profile pictures |
| 4:5 | 1080 × 1350 | Instagram portrait posts |
| 4:3 | 1600 × 1200 | Many phone photos, iPads, older screens |
| 3:2 | 6000 × 4000 | Most camera photos, 6 × 4 inch prints |
| 21:9 | 2560 × 1080 | Ultrawide monitors, cinema |
How to calculate it
- Find the greatest common divisor of the width and height. For 1920 and 1080 it's 120.
- Divide both: 1920 ÷ 120 = 16 and 1080 ÷ 120 = 9.
- The ratio is 16:9.
Resize without stretching
Keep the ratio the same:
new height = new width × original height ÷ original width
Example: a 4000 × 3000 photo resized to 1200 wide is 1200 × 3000 ÷ 4000 = 900 high.
Step by step
- Open the aspect ratio calculator.
- Type a width and height, pick a common ratio, or drop an image to use its size.
- Type a new width or height and the other one is filled in.
Change the ratio of an image or video
- Images: crop image to the new shape, then resize.
- Video: crop video to 1:1, 9:16, 4:5 or 16:9.
- Social posts: the social media image resizer does both.
Questions
What aspect ratio is 1920 × 1080?
16:9, the standard widescreen ratio.
Is 1080 × 1350 4:5?
Yes. 1080 ÷ 270 = 4 and 1350 ÷ 270 = 5.
Try it now
Find the aspect ratio of any width and height, or work out the missing width or height to resize without stretching.
Open aspect ratio calculator