How to read an aspect ratio
An aspect ratio is written as two numbers separated by a colon, such as 4 by 3 or 16 by 9. The first number describes width and the second height in relative terms.
Any pixel size can reduce to the same shape. Both 1,600 by 1,200 and 800 by 600 simplify to 4 by 3, so they share a shape even though one holds four times as many pixels.
Common ratios and where they appear
Traditional cameras and older televisions used 4 by 3, while widescreen displays and video settled on 16 by 9. Square formats use 1 by 1, and phones in portrait mode often shoot 9 by 16.
Print and paper have their own shapes. A4 and Letter pages are close to but not identical with each other, which matters when an image is placed on a page without cropping.
- 4 by 3: classic cameras and some tablets
- 16 by 9: widescreen monitors and video
- 1 by 1: square social posts
- 3 by 2 and 2 by 3: common still camera frames
Keeping the shape while resizing
Scaling both dimensions by the same factor preserves the ratio, so the picture gets bigger or smaller without distortion. Forcing one dimension alone stretches the image and makes subjects look wrong.
Cropping is the other way to change shape, because it removes pixels from one edge. Filekind resize workflows use proportional scaling, and cropping itself is not offered as a tool today.