This tool calculates the missing dimension that preserves an aspect ratio — give it a ratio like 16:9 and one side, and it finds the other. It can also reduce two dimensions to their simplest ratio. Everything updates live in your browser.
How to use it
- Enter an aspect ratio (e.g. 16:9), or two known dimensions.
- Enter one dimension to solve for the other.
- The proportional result appears instantly.
About Aspect Ratio Calculator
Keeping the right proportions matters whenever you resize images, video, or layout boxes — stretch them and everything looks wrong. Working out the matching height for a given width at 16:9, or reducing 1920×1080 to its ratio, is quick arithmetic that this tool removes the friction from. Enter a ratio and one side to get the other, or two sides to get the ratio in simplest terms. It is handy for responsive design, thumbnails, video embeds and print. The calculation runs entirely in your browser.
FAQ
What is a common video aspect ratio?
16:9 is standard for modern video and displays; 4:3 is the older standard, and 1:1 is square.
Can it tell me the ratio of two dimensions?
Yes. Enter both dimensions and it reduces them to the simplest whole-number ratio.
How do I keep an image's aspect ratio when resizing?
Lock the ratio of width to height: if a 1920×1080 image (16:9) is resized to 1280 wide, the height must be 720 to avoid distortion. This calculator finds the missing dimension for any target size.