Aspect Ratio Calculator

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 and 1:1 are all reduced fractions of far larger pixel dimensions. 21:9 is the exception: it is a rounded name, and an ultrawide 2560×1080 screen really reduces to 64:27.

Common aspect ratios

Each opens this calculator on that ratio, with its usual resolutions — every one reduced to the ratio when the site is built — and where the shape is used:

• 9:16
• 2:3
• 3:4
• 4:5
• 1:1
• 4:3
• 3:2
• 16:10
• 16:9
• 21:9