Why does my 1 TB drive only show 931 GB?

The manufacturer sells it as 1 TB meaning 1,000,000,000,000 bytes, using decimal prefixes. Windows displays capacity in binary units but labels them GB, so it divides by 1,073,741,824 and reports about 931. The drive holds exactly what was advertised; the two systems just count differently.

What is the difference between GB and GiB?

A gigabyte (GB) is 1,000,000,000 bytes. A gibibyte (GiB) is 1,073,741,824 bytes, about 7.4% more. GiB is the unambiguous binary unit, introduced precisely because GB was being used for both meanings.

How many megabytes are in a gigabyte?

1000 MB in a decimal gigabyte. If you mean the binary sense, there are 1024 MiB in a GiB. Most file managers show the binary figure.

Why are internet speeds in megabits rather than megabytes?

Network throughput has always been measured in bits per second. A byte is 8 bits, so a 100 Mbps connection transfers at most about 12.5 MB per second. Watch the capitalisation: Mb is megabits, MB is megabytes.

Data Storage Converter - GB to MB, TB to GB, GiB vs GB

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Byte (B)

Decimal and binary prefixes

Digital storage is counted two different ways, and the two disagree by an amount that grows with size. Decimal prefixes follow SI: a kilobyte is 1000 bytes, a megabyte is 1000 kilobytes, and so on. Binary prefixes follow powers of two: a kibibyte (KiB) is 1024 bytes, a mebibyte (MiB) is 1024 KiB.

The gap starts at 2.4% for kilobytes and widens to roughly 10% by terabytes. This is the whole explanation for the most common storage complaint: a drive sold as “1 TB” holds 1,000,000,000,000 bytes, which Windows then reports as about 931 GB because it is actually counting gibibytes. Neither figure is wrong; they are different units wearing similar labels.

Drive manufacturers and network speeds use decimal. Operating system file sizes and RAM use binary. Both are listed here so you can convert between them directly.

Quick reference

Decimal versus binary at each scale

Decimal unit	Equivalent binary value
1 kB (1000 bytes)	0.9766 KiB
1 MB (1000 kB)	0.9537 MiB
1 GB (1000 MB)	0.9313 GiB
1 TB (1000 GB)	0.9095 TiB (931.32 GiB)
1 KiB	1024 bytes
1 MiB	1,048,576 bytes
1 GiB	1,073,741,824 bytes
1 byte	8 bits

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Questions

Frequently Asked Questions

Why does my 1 TB drive only show 931 GB?: The manufacturer sells it as 1 TB meaning 1,000,000,000,000 bytes, using decimal prefixes. Windows displays capacity in binary units but labels them GB, so it divides by 1,073,741,824 and reports about 931. The drive holds exactly what was advertised; the two systems just count differently.
What is the difference between GB and GiB?: A gigabyte (GB) is 1,000,000,000 bytes. A gibibyte (GiB) is 1,073,741,824 bytes, about 7.4% more. GiB is the unambiguous binary unit, introduced precisely because GB was being used for both meanings.
How many megabytes are in a gigabyte?: 1000 MB in a decimal gigabyte. If you mean the binary sense, there are 1024 MiB in a GiB. Most file managers show the binary figure.
Why are internet speeds in megabits rather than megabytes?: Network throughput has always been measured in bits per second. A byte is 8 bits, so a 100 Mbps connection transfers at most about 12.5 MB per second. Watch the capitalisation: Mb is megabits, MB is megabytes.