Aspect Ratio Calculator

An aspect ratio is the shape of a rectangle, written as width to height. A 1920 x 1080 video is 16:9, which means 16 units wide for every 9 units tall. This calculator simplifies any size to its ratio and finds a missing width or height for the ratio you need.

The tool has two modes. Calculate Ratio from Dimensions takes a width and height, divides both by their greatest common divisor (GCD), and shows the simplest whole-number ratio. It also shows the diagonal in pixels, the megapixels and whether the shape is landscape, portrait or square. Resize with Ratio Constraint works the other way: choose a ratio, type one side, and the other is filled in, rounded to whole pixels. Presets cover 16:9, 4:3, 21:9, 1:1, 3:2, 9:16, 5:4 and 2:1.

Exact math can surprise you. Many screens are sold under a rounded name. A 1366 x 768 laptop screen simplifies to 683:384, which is close to 16:9 but not equal. An ultrawide 2560 x 1080 monitor is exactly 64:27, although it is sold as 21:9. When a result looks odd, compare the decimal values instead: 16:9 is 1.778 and 1366 x 768 is 1.779.

Keeping the ratio fixed is what stops a picture from stretching. It is also why a 4:3 photo gets black bars or cropping in a 16:9 frame. Once you know the target size, the Image Resizer can scale the image. The Image Cropper cuts it to a new shape with ratio presets.