In short: An aspect ratio calculator keeps proportions when resizing: for a 16:9 ratio, height = width × 9 ÷ 16, so a 1920-pixel-wide frame is 1080 pixels tall.
About Aspect Ratio Calculator
Aspect ratio is the proportion between width and height. Video is usually 16:9 (1920×1080, 3840×2160), classic photos 3:2, older monitors and iPads 4:3, ultrawide displays 21:9 and vertical phone video 9:16. Keeping the ratio when you resize prevents images and video from being stretched or letterboxed.
Enter a ratio and either dimension and the other is calculated instantly, rounded to whole pixels. Or enter any resolution and the calculator reduces it with the greatest common divisor — 2560×1440 becomes 16:9 — and also shows it as a decimal (1.78:1), the way cinema formats are often described.
How to use Aspect Ratio Calculator
- Choose a preset ratio or enter your own.
- Type a width to get the height, or a height to get the width.
- Or enter both dimensions and press “Find ratio” to simplify them.
Examples
16:9 at 1280 px wide → 720 px tall.
4:5 at 1080 px wide → 1350 px tall.
Frequently asked questions
Is 1366×768 really 16:9?
Almost: it simplifies to 683:384 (1.779:1), which is marketed as 16:9 (1.778:1).
What ratio is 1080×1080?
1:1 (square).
Why does my result have decimals?
Some ratios do not divide evenly; heights and widths are rounded to the nearest pixel. Video encoders often prefer even numbers.
What is 1.91:1?
The landscape ratio used by Facebook and LinkedIn link previews, e.g. 1200×628.
Updated November 2026 · Free, no signup · How we build and test tools