Why your 1 TB drive shows up as 931 GB
A drive box says 1 TB. Plug it in, and the operating system reports something like 931 GB free. No capacity went missing — the box and the OS are using two different definitions of "giga" and "tera," one decimal and one binary, and the gap between them grows the bigger the number gets.
The method
Storage marketing uses decimal units, where each step is ×1,000: 1 KB = 1,000 bytes, 1 MB = 1,000,000 bytes, 1 GB = 1,000,000,000 bytes, 1 TB = 1,000,000,000,000 bytes. Operating systems typically report binary units, where each step is ×1,024: 1 KiB = 1,024 bytes, 1 MiB = 1,048,576 bytes, 1 GiB = 1,073,741,824 bytes. To compare the two, convert both to plain bytes first, then divide by whichever unit you want to land on.
A real example: a 1 TB drive, in GiB
1 TB in bytes is 1,000,000,000,000. One GiB is 1,073,741,824 bytes. Dividing: 1,000,000,000,000 ÷ 1,073,741,824 = 931.32, so a 1 TB drive reads as about 931 GB (really GiB, though most operating systems just label it "GB") in your file explorer. No storage is missing; it's the same bytes measured in a bigger-denominator unit.
A real example: an 8 GB flash drive, in GiB
8 GB in bytes is 8 × 1,000,000,000 = 8,000,000,000. Dividing by bytes-per-GiB: 8,000,000,000 ÷ 1,073,741,824 = 7.45, so an "8 GB" drive shows roughly 7.45 GB free before you've even copied a file onto it — the entire gap is unit definition, not a defect.
A real example: converting the other direction, 16 GiB of RAM into decimal GB
A laptop spec sheet says 16 GB of RAM; RAM is actually sized in binary units, so that 16 is really GiB. In bytes: 16 × 1,073,741,824 = 17,179,869,184. In decimal GB: 17,179,869,184 ÷ 1,000,000,000 = 17.18, so 16 GiB of RAM is about 17.18 decimal GB — the reverse of the drive example, because RAM capacity is conventionally stated in the binary unit while storage capacity is conventionally stated in the decimal one.
Why this isn't a scam
The international standard (IEC) names for these units — kibibyte (KiB), mebibyte (MiB), gibibyte (GiB) — exist specifically to separate the ×1,024 scale from the ×1,000 one, because the collision between "a kilobyte" meaning two different sizes long predates the standard. Drive and SSD capacities are listed in decimal because that's the SI definition of the prefixes; operating systems report in binary because memory addressing is naturally a power of two. Both are internally consistent; they just don't agree with each other.
Run your own numbers
The free Data Size Converter converts between bytes, bits, decimal KB/MB/GB/TB and binary KiB/MiB/GiB instantly, entirely on your device.