# Aspect ratio calculator: find and resize 16:9, 9:16, 4:5 and more

> Find the aspect ratio of a width and height, an image or a video, then work out the matching size at any width or height, with even numbers for video. Covers 16:9, 9:16, 1:1, 4:5 and 3:4.

URL: https://cutfac.com/tools/aspect-ratio-calculator  
Last updated: 2026-10-28  
Language: [한국어](https://cutfac.com/ko/tools/aspect-ratio-calculator)

Type a width and height, or read them from an image or video, to see its aspect ratio and the common ratio it's closest to. Then pick a ratio and a width to get the height that keeps the shape.

Runs in your browser. Nothing is uploaded.

## How to use it

1. **Enter a size.** Type a width and height, or read them from an image or video file. The file stays on your computer.
2. **Read the ratio.** See the ratio in whole numbers and as a decimal, and the common ratio it's closest to.
3. **Resize to a ratio.** Pick your ratio or a common one, type a new width or height, and get the other side.

## How an aspect ratio is worked out

An aspect ratio is width to height, divided down by the largest number that goes into both. 1920 × 1080 divides by 120 into 16:9; 1080 × 1350 divides by 270 into 4:5.

Some sizes don't reduce to small numbers. 1366 × 768, a common laptop screen, reduces to 683:384, which is 1.78:1 and 0.05% off 16:9, so it's called 16:9 in practice.

## Ratios for short-form and social video

The ratios below cover most of what you'll post. YouTube asks for 16:9 thumbnails, and Instagram keeps photo posts whole between 1.91:1 and 3:4.

- 9:16, 1080 × 1920: TikTok, Reels, Shorts and Stories.
- 16:9, 1920 × 1080 or 3840 × 2160: YouTube videos and thumbnails.
- 4:5, 1080 × 1350, and 3:4, 1080 × 1440: Instagram portrait posts.
- 1:1, 1080 × 1080: square posts.
- 1.91:1, 1080 × 566: Instagram landscape posts.

## Resizing without distortion

Changing one side by the ratio keeps the picture's shape. Moving to a different ratio, such as 16:9 footage into a 9:16 video, needs a crop or bars; stretching to fit distorts faces and text.

Video encoded as H.264 needs an even width and height, so switch on even numbers when the size is for a video export.

## Sources

- [YouTube Help: Add custom thumbnails on YouTube](https://support.google.com/youtube/answer/72431)
- [Instagram Help: Image resolution of photos you share on Instagram](https://help.instagram.com/1631821640426723)

## Questions

### How do I calculate an aspect ratio?

Divide the width and height by the largest number that divides both. 1920 and 1080 both divide by 120, giving 16:9.

### What sizes are 16:9?

1280 × 720, 1920 × 1080, 2560 × 1440 and 3840 × 2160 are the common ones.

### What ratio do TikTok, Reels and Shorts use?

9:16, vertical full screen. 1080 × 1920 is the usual export size.

### Why round to even numbers?

H.264 video needs an even width and height, so an odd size fails to export or gets trimmed. Images don't need it.

### Is my file uploaded?

No. When you read a size from a file, your browser only reads its width and height. Nothing is sent anywhere.