Aspect Ratio Calculator
Enter a ratio and one dimension to get the other, or enter both dimensions to find their ratio. Useful for images, video, presentations and prints.
How it works
An aspect ratio is the proportion between width and height. If the ratio is 16:9 and the width is 1920, the height is 1920 × 9 ÷ 16 = 1080.
- Missing dimension — enter the ratio and one side; the other is filled in automatically.
- Find a ratio — enter both sides and the simplified ratio is shown, e.g. 3840 × 2160 becomes 16:9.
- Area — width × height, handy for comparing pixel counts or paper sizes.
Frequently asked questions
What ratio should I use for video?
16:9 is the standard for most video and monitors. 21:9 is common for cinematic widescreen, 9:16 for vertical phone video, and 1:1 works everywhere for social posts.
Why is my ratio not simplifying to nice numbers?
If the two dimensions don't share a clean factor, the ratio stays awkward — for example 1000 × 600 simplifies to 5:3, but 999 × 600 does not simplify at all. The decimal value always tells you the exact proportion.
Does it work for physical sizes?
Yes. The math is unit-agnostic: millimetres, inches or points all work, as long as both dimensions use the same unit.
What is the difference between ratio and resolution?
Resolution is the exact pixel count, like 1920 × 1080. The aspect ratio is the shape that count describes, like 16:9. Many resolutions share one ratio.