Aspect Ratio Calculator
Calculate proportional width or height from any aspect ratio.
Overview
The Aspect Ratio Calculator gives you the missing dimension once you fix one side and a target ratio like 16:9, 4:3, 1:1 or 21:9. Type in a width and the height pops out — or vice versa — without any mental arithmetic.
It is the daily-driver tool for video editors resizing footage, web designers framing hero images and photographers preparing prints. If you've ever fudged a YouTube thumbnail to fit 1280 wide and it came out 721 high instead of 720, this tool stops that.
How it works
An aspect ratio like W:H is a proportion, so if you know one side the other comes from cross-multiplication. Given target ratio w:h and a known width W, the height is H = W * h / w. Given a known height H, the width is W = H * w / h.
The calculator also normalises ratios via the greatest common divisor — 1920:1080 simplifies to 16:9 for example — so you can paste raw resolutions and recognise the canonical ratio at a glance.
Examples
Ratio 16:9, width 1920 → height 1080
Ratio 4:3, height 600 → width 800
Ratio 21:9, width 3440 → height ≈ 1474.3
Reduce 2560:1440 → 16:9
FAQ
What's the difference between 16:9 and 16/9?
Same thing — the colon is the conventional written form, the slash is the decimal value (1.7778).
Why does my calculated height have a fraction?
Pixel dimensions must be integers, so the ratio sometimes can't be matched exactly. Round to the nearest integer or pick a resolution that divides evenly.
Is 1.85:1 a valid input?
Yes — the calculator handles non-integer ratios used in cinema, like 1.85:1 (US theatrical) and 2.39:1 (CinemaScope).
How do I find the ratio of an existing image?
Enter both dimensions and let the calculator reduce them via GCD. 1366:768 for instance reduces to a non-standard 683:384, close to but not exactly 16:9.
Does aspect ratio depend on orientation?
Yes. A 9:16 portrait video has the same shape as a 16:9 landscape rotated 90 degrees. Swap the ratio when you swap orientation.