What compression ratio ranges are used for lossy formats?

In this year’s Web Almanac Media chapter, we published per-format median bit-per-pixel numbers, but not per-format distributions. This has come up a couple of times in conversations since the Almanac was published, specifically for lossy formats. So I figured a few of those distributions were worth publishing somewhere. Here seemed like a good place!


Distribution of JPEG bits_pixel
Distribution of WebP bits_pixel
Distribution of AVIF bits_pixel

TL;DR most lossy images on the web are compressed to between ~0.5 and 3.75 bits per pixel. JPEG covers the higher end of that range (p25 1.22 → p75 3.76); AVIF covers the lower end (p25 0.49 → p75 1.79). WebP is somewhere in the middle.

As we mentioned in the chapter, there are many more JPEGs than either WebPs or AVIFs, and many of those JPEGs were compressed many years ago, with legacy software. Modern JPEG encoders do better than this, but this is a ~complete survey of the state of the web, legacy content and all.