What aspect ratio means
Aspect ratio is the shape of an image or video: its width compared to its height. A ratio of 16:9 means 16 units wide for every 9 tall, whatever the actual size. 1920 × 1080 and 3840 × 2160 are both 16:9; one is just bigger.
To find a ratio, divide both sides by the largest number that goes into both. The calculator does this for you, and when a size doesn't simplify neatly, like 1366 × 768, it tells you the common ratio it's close to.
Ratios are sometimes written as one number against 1, like 1.78:1 for 16:9 or 2.39:1 for widescreen film. The calculator shows both forms, so you can match whichever one a platform or editor asks for.
Common ratios and where they're used
These cover most of what creators need:
- 16:9: YouTube videos, TVs and most laptop screens. 1920 × 1080 is full HD.
- 9:16: Reels, TikTok, YouTube Shorts and Stories. 1080 × 1920 is the usual size.
- 4:5: Instagram portrait feed posts, at 1080 × 1350.
- 1:1: square posts and profile pictures, often 1080 × 1080.
- 4:3: the default shape of many phone cameras and iPads.
- 3:2: most DSLR and mirrorless camera photos, and 4 × 6 inch prints.
- 21:9: ultrawide monitors and a cinematic look, though screens sold as 21:9 are often a little wider.
Working out a missing side
To keep a ratio, multiply the side you know by the other side of the ratio, then divide by its matching side. For 16:9 at 1280 wide: 1280 × 9 ÷ 16 = 720 tall. For 9:16 at 1080 wide: 1080 × 16 ÷ 9 = 1920 tall.
If the answer isn't a whole number, the calculator rounds it and shows the exact value. For video, round to an even number, because many encoders expect even dimensions.
Changing ratio without stretching
Going from one ratio to another, like turning a 16:9 video into 9:16, always means cropping or adding space. Stretching it to fit makes people look squashed. Crop if the subject is in the middle, or fit it inside the new shape with a background if nothing can be cut. The image resizer can do either for photos.
If you plan to post the same video in several shapes, film with room around the subject. A centered subject with space on every side crops cleanly to 16:9, 1:1, 4:5 and 9:16.
Frequently asked questions
How do I calculate aspect ratio?
Divide the width and height by their greatest common divisor. For 1920 × 1080 that's 120, giving 16:9. Enter the size above and the calculator does it.
What is 16:9 in pixels?
Common 16:9 sizes are 1280 × 720 (HD), 1920 × 1080 (full HD), 2560 × 1440 and 3840 × 2160 (4K UHD).
What aspect ratio is 1080 × 1350?
4:5. It's the tallest shape Instagram allows for feed photos, which is why it's popular for posts.
What's the difference between 9:16 and 16:9?
Same shape, turned on its side. 16:9 is landscape, for YouTube and TVs; 9:16 is portrait, for Reels, TikTok, Shorts and Stories.