MB vs MiB: why a 1 TB drive shows up as 931 GB

A drive sold as 1 TB can show roughly 931 GB in Windows because the label and the display use different units. The advertised capacity is one trillion bytes. Expressed in binary units, that is about 931 GiB, even when the screen labels it “GB”.

That explains the unit difference. It does not mean all of the capacity is free for your files: partitions, formatting, recovery space and existing data can reduce the amount available.

Compare the units before comparing the numbers

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

The i makes the binary unit explicit. MiB means mebibytes and GiB means gibibytes. Software that says only KB, MB or GB may use either convention, so check its documentation or the byte count when the distinction matters.

In the file size converter, enter 1 and select TB. Compare the GiB result, about 931.32, with the TiB result, about 0.9095. They describe the same capacity at different scales.

Check a drive that seems short of space

Start by distinguishing total capacity from free space. Free space falls as you save files; the decimal-to-binary conversion does not.

For reference, advertised capacities convert approximately as follows, before filesystem and partition overhead:

• 500 GB → 465.66 GiB
• 1 TB → 931.32 GiB
• 2 TB → 1862.65 GiB
• 4 TB → 3725.29 GiB

If the total shown is much lower than that, check whether you are viewing one partition rather than the whole drive. Unallocated space and recovery partitions are separate from the unit conversion. These numbers alone cannot establish that a drive is healthy or has its advertised capacity.

Upload limits can use either convention

A limit described as “10 MB” might mean 10,000,000 bytes or 10,485,760 bytes. A file close to the limit can pass one interpretation and fail the other.

Use the receiving service’s definition if it provides one. Otherwise, leave some room below the displayed limit. The converter shows both unit families so you can compare them without guessing.

Operating-system conventions also vary by application. Windows commonly uses binary calculations with decimal-looking labels; macOS commonly reports drive storage in decimal units. Linux utilities and file managers can use different defaults. The label on one screen is not a rule for every program on that machine.

Mbps is a speed in bits, not bytes

An advertised 100 Mbps connection means 100 million bits per second. Divide by eight to get 12.5 MB/s, or about 11.92 MiB/s.

Those are unit conversions, not promised download speeds. Network overhead, Wi-Fi conditions, the server and other traffic can reduce the rate. The converter’s download-time estimate assumes the selected rate is sustained throughout the transfer.

How the drive calculation works

To convert bytes to GiB, divide by 1,073,741,824:

1,000,000,000,000 bytes ÷ 1,073,741,824 = about 931.32 GiB

The IEC introduced separate binary prefixes to avoid using “mega” and “giga” for two quantities. The names are precise; everyday labels remain inconsistent. When comparing two files or drives, converting both to bytes removes that ambiguity.

Source

• NIST — prefixes for binary multiples, including the IEC definitions

Last reviewed 2 October 2026.