Why a 1 TB drive shows up as 931 GB

Two meanings of the same word

In decimal units, which manufacturers and network providers use, a kilobyte is 1,000 bytes, a megabyte 1,000 kilobytes and so on, so 1 TB is 1,000,000,000,000 bytes. In binary units, which memory and many operating systems use, each step is 1,024, so one gigabyte is 1,073,741,824 bytes.

Divide 1,000,000,000,000 by 1,073,741,824 and you get 931.3. The same number of bytes is a terabyte in one system and about 931 gigabytes in the other.

More examples

A 500 GB drive shows about 465.7 GB in binary terms. A 5,000,000-byte file is 5 MB in decimal and about 4.77 MB in binary. The gap widens as units grow: about 2.4% at kilobytes, about 7% at gigabytes and about 10% at terabytes.

Who reports what

Windows shows binary sizes using the labels GB and TB, while macOS reports decimal. That is why one drive can read differently on two machines. Proper binary names exist, such as GiB and TiB, but most software does not use them, which is the source of the confusion.

Why it matters for upload limits

Some upload forms count 1 KB as 1,000 bytes and some as 1,024, so a file close to the limit can pass on one and fail on another. When you are near a limit, convert in both modes and aim for a size that passes under either. The same applies to cloud storage and download quotas.

Do not mix megabits and megabytes

Internet speeds are quoted in megabits per second, and storage in megabytes. There are eight bits in a byte, so a 100 Mbps connection moves at most about 12.5 MB per second in decimal terms. Real speeds are lower once overhead is included.