ToolzAspect Ratio Calculator
Find a missing width or height from a ratio, or simplify dimensions to a ratio.
Height
1080
What an aspect ratio actually describes
An aspect ratio like 16:9 is a proportion, not a size — it says the width is 16 units for every 9 units of height, without fixing what a unit is. A 1920×1080 screen and a 320×180 thumbnail share the same ratio because 1920:1080 and 320:180 both reduce to 16:9. That is why resizing something without preserving its ratio is what stretches or squashes it.
Finding a missing width or height
Once a ratio is fixed, one known dimension is enough to solve for the other: divide the known side by its share of the ratio, then multiply by the other share. Enter a ratio and the width or height you already have, and the missing side is computed for you — useful for cropping an image to 16:9 from a known width, or fitting a video into a container of a set height.
Reducing a ratio to its simplest form
Going the other way — from raw pixel dimensions to a clean ratio like 16:9 or 4:3 — means dividing both numbers by their greatest common divisor. 1920 and 1080 share a GCD of 120, so 1920:1080 reduces to 16:9. Common video and photo ratios such as 16:9, 4:3, 3:2, 1:1 and 21:9 are all reduced fractions of far larger pixel dimensions.