Why your 1 TB drive shows only 931 GB
Nobody stole your storage. Drive makers and Windows are counting with different definitions of the same word, and both are technically right.
4 min read · Reviewed July 2026
You buy a 1 terabyte drive, plug it in, and Windows reports 931 gigabytes. Every year, thousands of people return perfectly good drives over this. Nothing is missing. The manufacturer and your operating system are using two different meanings of ‘gigabyte,’ and the gap between them compounds as sizes grow.
Decimal versus binary counting
Drive makers count the way the metric system counts: 1 TB = 1,000,000,000,000 bytes. Clean powers of ten. Computers, though, address memory in powers of two, so software historically counted 1 ‘GB’ as 1,073,741,824 bytes (2 to the 30th). Same word, two numbers, about a 7% gap at the terabyte scale.
Your 1 TB drive holds exactly one trillion bytes. Divide by the binary gigabyte and you get 931 — the number Windows shows. The drive is full-sized; the units are quarreling.
GiB exists to end the argument (nobody uses it)
Standards bodies fixed this back in 1998: decimal units keep the old names (gigabyte, GB), and binary units get new ones — gibibyte (GiB), tebibyte (TiB). macOS and Linux mostly complied; macOS reports your drive in decimal GB and the numbers match the box. Windows still counts in binary while displaying ‘GB,’ which is why the confusion refuses to die. My take: the drive makers are following the standard, and Windows’ labeling is the actual bug.
Check it yourself
Our converter’s Data category has both unit families. Type 1 TB and convert to GiB — you’ll get 931.32, the exact number from your file manager. RAM, by the way, is genuinely binary (16 GB of RAM really is 16 GiB), and internet speeds are decimal bits, not bytes — a 1 gigabit connection tops out around 125 decimal megabytes per second. The units are a minefield; the converter is the map.