"Why does my 1TB drive show up as 931GB?" is one of the most common storage-related questions, and the answer comes down to two different, equally valid definitions of the same units.
Two competing definitions of the same prefix
Storage manufacturers typically use decimal (SI) units, where 1 kilobyte = 1,000 bytes, 1 megabyte = 1,000 kilobytes, and so on in clean powers of ten — this matches how every other metric prefix works. Operating systems, however, have historically calculated file sizes using binary units, where 1 kilobyte = 1,024 bytes (2^10), because computers fundamentally operate in powers of two.
Why this creates the "missing" storage
A drive advertised as "1 terabyte" using the manufacturer's decimal definition (1,000,000,000,000 bytes) shows up as roughly 931 "gibibytes" when your operating system calculates and displays it using binary math — the storage isn't actually missing at all; it's the identical number of bytes, just measured against two different-sized rulers.
The proper terms for each
To resolve exactly this ambiguity, the International Electrotechnical Commission introduced binary-specific prefixes — kibibyte (KiB), mebibyte (MiB), gibibyte (GiB) — for the 1,024-based units, distinct from kilobyte (KB), megabyte (MB) and gigabyte (GB) for the 1,000-based ones. In practice, though, most consumer software still labels binary values with the decimal unit names, which is exactly what keeps causing the confusion.
Convert between the two correctly
A data storage converter that clearly distinguishes 1000-based and 1024-based units avoids assuming one convention when your actual number might be using the other.
The bottom line
No storage is actually "missing" — it's a genuine, longstanding naming ambiguity between two different, both technically legitimate definitions of the same unit prefixes.
Try it yourself
Put this into practice with our data storage converter.