Going from width and height to a ratio, the calculator divides both numbers by their greatest common divisor to reduce them to the simplest whole-number form — for example, 1920×1080 reduces to 16:9, the standard widescreen ratio.
Going the other direction, pick a ratio (or a preset like 16:9 or 4:3) and enter either the width or the height, and the calculator scales the missing dimension so that width ÷ height stays exactly equal to your chosen ratio.
The values you enter are treated as plain numbers — pixels, centimetres, inches, or any other consistent unit — since only the proportion between them matters for an aspect ratio, not the specific unit of measurement.
By dividing both the width and height by their greatest common divisor, reducing them to the smallest whole numbers that keep the same proportion — 1920×1080 both divide evenly by 120, giving 16:9.
Yes — enter your target ratio and one known dimension (width or height), and the calculator works out what the other dimension needs to be to match that exact ratio.
No — aspect ratio is a pure proportion between two numbers, so any consistent unit works as long as you use the same unit for both width and height.
Standard presets like 16:9 (widescreen video), 4:3 (traditional TV/photo), 1:1 (square), and 21:9 (ultrawide) are typically included alongside the option to enter a fully custom ratio.
