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Tools / Aspect ratio calculator

Aspect ratio calculator

Reduces any width and height to their simplest ratio, then works out the matching height for a new width. Useful for video exports, responsive images and anything that must not end up stretched.

Runs entirely in your browser

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About this tool

Aspect ratio is the relationship between width and height, and keeping it constant is what stops images and video from looking stretched or squashed. This tool reduces any width and height to their simplest ratio — turning 1920×1080 into 16:9, for example — and then works out the matching height (or width) for a new size, so a resize preserves the proportions exactly.

That is exactly what you need when exporting video at a different resolution, generating responsive image sizes, or fitting content into a frame without distortion. Give it the original dimensions and one dimension of the target, and it fills in the other so nothing is deformed.

It runs in your browser, so it is instant and requires no upload. Use it whenever a resize must stay true to the original shape rather than being eyeballed.

Frequently asked questions

What is an aspect ratio?
It is the proportional relationship between width and height, written like 16:9 or 4:3. Keeping it constant when resizing prevents images and video from being stretched.
How do I resize without distortion?
Enter the original width and height and the new width (or height), and the tool calculates the other dimension so the ratio is preserved and the content is not deformed.
What does “simplest ratio” mean?
It reduces the two dimensions by their greatest common divisor, so 1920×1080 becomes 16:9 — the smallest whole-number expression of the same proportion.
What is 16:9 used for?
16:9 is the standard widescreen ratio for most modern video, monitors and TVs. The tool can express any dimensions as a ratio, not just common ones.
Does it upload my images?
No. It works purely with the numbers you enter, in your browser, so nothing is uploaded.

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