Aspect ratio
Missing dimension and reduced ratio
Missing dimension
Fill one dimension, the other is computed.
Simplify dimensions
This aspect-ratio tool works both ways. Pick a common ratio (16:9, 4:3, 21:9, 1:1, 3:2) or type your own, then enter a single dimension: the other is computed automatically to keep the proportions. Conversely, enter an actual width and height and the tool simplifies them into a reduced ratio (using the GCD) and a decimal ratio. Handy for resizing images, videos, screens or mockups.
Everything is computed in your browser: no dimension is sent, no tracking, no ads.
FAQ
How do I find the missing dimension?
Pick a ratio then enter the width OR the height: the other value is derived to match the ratio.
How is a ratio simplified?
With the greatest common divisor (GCD) of width and height, e.g. 1920×1080 becomes 16:9.
Can I use a custom ratio?
Yes, enter it in W:H format (for example 16:10) in the dedicated field.
Are my dimensions sent online?
No, the calculation is entirely local in your browser.