How to calculate an aspect ratio
Quick answer
To calculate an aspect ratio, divide the width and the height by their greatest common divisor. 1920 by 1080 is 16:9. The Aspect ratio calculator does it for you, and also finds the missing side when you want to keep a ratio.
Steps
- Open the Aspect ratio calculator and type a width and a height in pixels. The simplest ratio appears.
- To resize to a ratio, pick one such as 16:9, 4:3 or 1:1, or type your own.
- Type the new width and the height follows, or type the height and the width follows.
- Use those numbers in the Resize images or Crop images tool.
Common ratios and where they are used
Square 1:1 is used for profile pictures. 16:9 is video and most screens, 4:3 is older screens and many cameras, and 3:2 is SLR cameras and 4 by 6 inch prints. 9:16 is stories and short video, and 4:5 is Instagram portrait posts.
The calculator lists them with what they are used for, so you can pick the one a place asks for.
When a size is only close to a ratio
Some sizes are almost, but not exactly, a common ratio. 1366 by 768 is 683:384, which is within a fraction of a percent of 16:9. The calculator shows both so you know it is close rather than exact.
Heights and widths are rounded to a whole pixel when you resize to a ratio.
Common questions
What is the aspect ratio of 1920 x 1080?
16:9. Divide both by 120, their greatest common divisor, and you get 16 and 9.
How do I keep the ratio when I resize?
Choose the ratio and type the new width. The height is worked out as width times the ratio height divided by the ratio width.
Does this change my picture?
No. It is a calculator and uses no file.
Written by Basic App Company. Last checked against the tool on 12 November 2026. The tool runs in your browser, so your pictures are not uploaded.