# Aspect ratio calculator for video sizes

Type a width and a height to get their aspect ratio, or pick a ratio (16:9, 9:16, 1:1, 4:5 or your own) and type one side to get the other, rounded to the even numbers a video encoder needs. With the common video sizes for each ratio. Free, no sign-up.

Use it at https://opusmotion.com/tools/aspect-ratio-calculator.

## How to use it

1. To find a ratio, type the width and the height, like 1920 and 1080: the calculator gives 16:9, the ratio as a number and the closest common ratio.
2. To find a size, pick a ratio and type the width or the height: the other side appears, with the even size for video next to it.
3. Copy the size you need, or take one of the common sizes listed under each ratio.

## Questions

### How do I calculate an aspect ratio?

Divide the width and the height by their greatest common divisor. For 1920 × 1080 it's 120, which leaves 16:9. The calculator does it as you type, and also gives the ratio as one number (1920 ÷ 1080 ≈ 1.778).

### How do I get the height for a width at a given ratio?

Multiply the width by the second number of the ratio and divide by the first: at 16:9, a width of 1280 gives 1280 × 9 ÷ 16 = 720. At 9:16, the same width gives 2275.6, which the calculator rounds to 2276 for video.

### What sizes are 16:9 and 9:16?

16:9 is the horizontal shape of most screens and videos: 1280 × 720, 1920 × 1080 and 3840 × 2160 are its usual sizes. 9:16 is the same turned upright, the vertical video of phones: 720 × 1280, 1080 × 1920 and 2160 × 3840.

### Why does a video size have to be an even number?

Most videos store color at half the width and half the height of the picture (4:2:0), so encoders like H.264 need both sides to be even. The calculator shows the exact result and the even size next to it.

### Is 1366 × 768 a 16:9 size?

Almost. Its exact ratio is 683:384, about 1.779, and 16:9 is about 1.778, so it shows as 16:9 to within 0.1%. Many sizes are rounded like that; the calculator tells you how far a size is from the closest common ratio.

### Which ratio should a video for social media be?

Vertical 9:16 for stories, reels and shorts, square 1:1 or vertical 4:5 for feeds, and 16:9 for YouTube and the web. Each platform's own numbers, with their sources, are in the social media video sizes guide.

## More free tools

- [Social media video sizes](https://opusmotion.com/tools/social-media-video-sizes.md): The video and image sizes of YouTube, TikTok, Instagram, Facebook, X, LinkedIn and Pinterest, each with its source
- [Resize video](https://opusmotion.com/tools/resize-video.md): Change a video's aspect ratio to 16:9, 9:16, 1:1 or 4:5, on a blurred or colored background
- [Crop video](https://opusmotion.com/tools/crop-video.md): Cut the frame down to 9:16, 1:1, 4:5, 16:9 or any shape, with a rectangle you drag
- [All free tools](https://opusmotion.com/tools.md)