How to calculate an aspect ratio
The aspect ratio is the proportion between width and height. To find it, divide both numbers by their greatest common divisor.
For 1920 × 1080 the greatest common divisor is 120. Then 1920 ÷ 120 = 16 and 1080 ÷ 120 = 9, so the ratio is 16:9.
How to resize without stretching
Keep the ratio fixed and calculate the missing side:
new height = new width × original height ÷ original width
Example: a 1920 × 1080 image scaled to 1280 pixels wide needs a height of 1280 × 1080 ÷ 1920 = 720 pixels.
Common aspect ratios
| Ratio | Typical use | Example sizes |
|---|---|---|
| 16:9 | HD and 4K video, YouTube, most monitors and TVs | 1280 × 720, 1920 × 1080, 3840 × 2160 |
| 9:16 | Vertical video: Reels, TikTok, Shorts, Stories | 1080 × 1920 |
| 4:3 | Older TVs and monitors, iPad, slide decks | 1024 × 768, 1600 × 1200 |
| 3:2 | Camera photos, 35mm film | 3000 × 2000, 6000 × 4000 |
| 1:1 | Square posts, profile pictures | 1080 × 1080 |
| 4:5 | Instagram portrait posts | 1080 × 1350 |
| 16:10 | Some laptops and productivity monitors | 1920 × 1200, 2560 × 1600 |
| 21:9 | Ultrawide monitors, cinema-style video | 2560 × 1080, 3440 × 1440 |
Questions
What is an aspect ratio?
An aspect ratio is the proportion between the width and the height of an image, video or screen. A 1920 × 1080 image has a ratio of 16:9, which means it is 16 units wide for every 9 units tall.
How do I calculate an aspect ratio?
Divide the width and the height by their greatest common divisor. For 1920 × 1080 the greatest common divisor is 120, so 1920 ÷ 120 = 16 and 1080 ÷ 120 = 9, giving 16:9.
How do I resize an image without stretching it?
Multiply the new width by the original height and divide by the original width. To shrink a 1920 × 1080 image to 1280 pixels wide, the height is 1280 × 1080 ÷ 1920 = 720.
Why does my result show an approximate ratio?
Some sizes, such as 1366 × 768, do not reduce to small whole numbers. When the size is within about 1.5% of a common ratio, the calculator shows that common ratio with a ≈ sign and lists the exact one beneath it.
Is 4K the same as 16:9?
Consumer 4K (UHD) at 3840 × 2160 is 16:9. Cinema 4K (DCI) at 4096 × 2160 is slightly wider, about 1.9:1.
Does this tool upload my images?
No. You only type numbers, and all calculations run in your browser. Nothing is uploaded.