For SSD-based M.2 modules, the most commonly occurring sizes are 22mm wide x30mm long, 22mm x 42mm, 22mm x 60mm, 22mm x 80mm and 22mm x 110mm. The cards will be called after their dimensions above: The first 2 digits define Width (all 22mm) and the remaining digits define Length from 30mm up to 110mm long. So, the M.2 SSDs are specified as 2230, 2242, 2260, 2280 and 22110

The picture below shows a 2.5-inch SSD and a 2242, 2260, and 2280 M.2 SSDs:

Size range image