What an aspect ratio is

An aspect ratio is the relationship between an image's width and height, written as width:height. A 1080 × 1350 image and a 2160 × 2700 image are both 4:5: same shape, different size. Platforms crop or letterbox images whose ratio does not match the slot they go into, which is why getting the ratio right matters more than the exact pixel count.

Common ratios and where they are used

The ratios people need most:

  • 1:1: square posts and product images.
  • 4:5: Instagram portrait posts, the tallest feed format.
  • 9:16: Stories, Reels, TikTok and other full-screen vertical formats.
  • 16:9: YouTube thumbnails, video and most screens.
  • 4:3 and 3:2: the native shape of most phone and camera photos.
  • 2:3: Pinterest pins.

Changing the ratio of many images

Changing a ratio means cropping (cutting part of the image) or padding (adding space around it). For a single image, any editor works. For a folder of photos that all need the same ratio and size, use a batch resizer with fill or fit modes so every file is handled the same way. Operimage does this for whole folders on a Mac, with presets for the common social ratios.

FAQ

How do I calculate an aspect ratio?

Divide width and height by their greatest common divisor. For 1920 × 1080 the divisor is 120, so the ratio is 16:9.

What height do I need for a 4:5 image 1080 pixels wide?

1350 pixels. Multiply the width by 5 and divide by 4.

What ratio are iPhone photos?

By default 4:3 (for example 4032 × 3024). Other modes such as 16:9 or square can be chosen in the Camera app.

Does changing the ratio reduce quality?

Cropping removes pixels at the edges but does not blur the rest. Stretching an image to a new ratio distorts it, so crop or pad instead.