Aspect Ratio Calculator
Work out aspect ratios and resize dimensions — simplify a size to 16:9, or find the missing width or height. In your browser.
🔒 Calculated in your browser. Editing width or height keeps the ratio; edit the ratio to recompute.
Keep the right proportions
Set a ratio (like 16:9) and enter a width to get the matching height, or a height to get the width — the other value updates automatically. You can also paste any size to simplify it to its smallest ratio and load it back in. Great for video, images, screens and responsive layouts.
How it works
A size is reduced to its simplest ratio using the greatest common divisor, so 1920×1080 becomes 16:9. Resizing then scales one dimension from the other while keeping that ratio exact.
Frequently asked questions
How is the ratio simplified?
The width and height are divided by their greatest common divisor, giving the smallest whole-number ratio (e.g. 1280×720 → 16:9).
Can I resize keeping the ratio?
Yes. Set the ratio, then type a new width or height and the other dimension is calculated to match.
Is anything uploaded?
No. All the maths runs in your browser.