Why your drive’s usable capacity appears smaller than advertised

A drive can show less usable storage than its advertised capacity because manufacturers and software often count bytes differently. The mismatch can look like missing space, but in many cases the drive has not lost capacity; understanding the difference helps explain what buyers can expect.

Manufacturers commonly use decimal units, where a gigabyte is one billion bytes, while Windows uses binary calculations, making a marketed 1TB drive appear as about 931GB. macOS reports the decimal figure, so the same drive may display differently across systems. Usable space can also be reduced by the operating system: the article cites iOS 27 taking over 22GB on a 128GB iPhone 16 Pro and Windows 11 using over 81GB on one gaming laptop.