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Aspect Ratio Calculator
Width, height and ratio from any two.
Free. Runs in your browser: nothing you enter or open is uploaded.
Find the ratio of a size
Work out the missing side
CSS
Common ratios
| Ratio | Decimal | Common sizes | Used for | Apply |
|---|
Ratios are reduced with the greatest common divisor. Sizes that do not reduce neatly, such as 1366 by 768, are also shown against the closest common ratio.
How to use it
- Type a width and height to see their ratio in its simplest form and as a decimal.
- To resize, pick a ratio and enter either a width or a height; the other side is filled in for you.
- Copy the CSS aspect-ratio line, or click Use on a common ratio to apply it.
Questions
How do I calculate an aspect ratio?
Divide the width and the height by their greatest common divisor. 1920 by 1080 share a divisor of 120, which gives 16 by 9.
What aspect ratio should I use for video?
16:9 for YouTube and most screens, 9:16 for Stories, Reels and Shorts, and 4:5 or 1:1 for feed posts on Instagram and Facebook.
What does the CSS aspect-ratio property do?
It keeps an element at a fixed shape while its width changes, so a video embed or image placeholder never jumps when the page loads. Set a width and aspect-ratio: 16 / 9 and the browser works out the height.