Why does a 1 TB hard drive show as 931 GB?

The manufacturer counts a terabyte as one trillion bytes, while Windows divides by 1,099,511,627,776 and still labels the result GB. Both describe the same drive; no space is missing.

How many megabytes are in a gigabyte?

1,000 megabytes using decimal units, or 1,024 mebibytes in a gibibyte using binary units. Which applies depends on the source.

What is the difference between Mbps and MB/s?

Mbps is megabits per second and MB/s is megabytes per second. There are eight bits in a byte, so divide the advertised connection speed by eight to get the download rate.

Data Storage Converter — MB, GB, TB, GiB, TiB

Data storage has two competing definitions of the same prefixes, and the disagreement is why a "1 TB" drive shows up as 931 GB when you plug it in. Nothing is missing and nobody is cheating. The drive and the operating system are counting in different bases.

The short version. Storage manufacturers use decimal units: 1 TB = 1,000,000,000,000 bytes. Windows displays binary units but labels them with decimal names, so it divides by 1,099,511,627,776 and prints "931 GB". Both numbers describe the same drive.

Quick reference

The table follows whichever units you select above.

Decimal and binary prefixes

Decimal	Bytes	Binary	Bytes
1 kB	1,000	1 KiB	1,024
1 MB	10⁶	1 MiB	1,048,576
1 GB	10⁹	1 GiB	1,073,741,824
1 TB	10¹²	1 TiB	1,099,511,627,776

The binary prefixes — kibi, mebi, gibi, tebi — were standardised by the IEC in 1998 precisely to end this confusion. Linux and macOS largely adopted them or switched to true decimal reporting. Windows did neither, and still shows binary quantities under decimal labels.

The gap widens as the units grow. At kilobytes it is 2.4 per cent. At terabytes it is nearly 10 per cent, which is exactly the "missing" space on a new drive.

Bits versus bytes

A byte is eight bits, and the distinction matters most for internet speeds. Connections are sold in megabits per second (Mbps); files download in megabytes per second (MB/s). Divide by eight to go from the advertised figure to the one your download manager shows.

A 100 Mbps connection therefore tops out around 12.5 MB/s, and that is before protocol overhead. People who feel their connection is a eighth as fast as promised are usually comparing the two units.

Common questions

Why does my 1 TB drive show 931 GB?

Because the manufacturer counted 10¹² bytes and your operating system divided by 2⁴⁰. 10¹² ÷ 1,099,511,627,776 is 0.909, so 1 TB displays as about 931 GiB — which Windows labels "GB". The space is all there.

How many MB in a GB?

1,000 using decimal units, or 1,024 if the source means MiB in a GiB. Which one depends on who wrote the number.

How fast is 100 Mbps in MB/s?

12.5 MB/s in theory, typically 11 to 12 in practice after overhead.

Data storage converter