Is a kilobyte 1,000 or 1,024 bytes?

By the SI definition, 1,000. A kibibyte (KiB) is 1,024 bytes. In older usage, kilobyte was often used for 1,024.

Why do drive makers use decimal units?

They follow the SI prefixes, in which kilo means 1,000, and that makes the number on the box larger.

How do I convert Mbps to MB per second?

Divide by 8. 100 Mbps is 12.5 MB per second.

Kilobytes vs Kibibytes: Why a 1 TB Drive Shows Less

Storage makers count in thousands, while some software counts in 1,024s. Both are right, and the units have different names.

By Editorial Team · Updated September 19, 2026 · 1 min read

Buy a 1 terabyte drive, plug it in, and your computer may report about 931 GB. Nothing is missing. Two different ways of counting are being used, and they are often labelled with the same name.

Two ways to count

Computer memory is built on powers of two, so 1,024 (2 to the power 10) has long been a convenient size. Before standard names existed, "kilobyte" was used for both 1,000 and 1,024 bytes.

To remove the ambiguity, the International Electrotechnical Commission introduced separate binary prefixes in the late 1990s.

Decimal (SI)	Value	Binary (IEC)	Value
kilobyte, KB	1,000 bytes	kibibyte, KiB	1,024 bytes
megabyte, MB	1,000,000 bytes	mebibyte, MiB	1,048,576 bytes
gigabyte, GB	10⁹ bytes	gibibyte, GiB	1,073,741,824 bytes
terabyte, TB	10¹² bytes	tebibyte, TiB	1,099,511,627,776 bytes

Where the 931 comes from

Drive makers use decimal units: 1 TB is 1,000,000,000,000 bytes. If software reports the size in binary units but still labels them "GB", it divides by 1,024³ (1,073,741,824):

1,000,000,000,000 ÷ 1,073,741,824 = 931.32

So a 1 TB drive holds 931.32 GiB. The gap grows with size: at kilobytes it is 2.4%, at terabytes about 9%.

Which operating systems do what

Practice varies. Some systems, such as macOS, show decimal units, matching the drive's label. Others have historically shown binary sizes under the decimal names. Check whether a tool says GB or GiB, and what it means.

Bits and bytes

A byte is 8 bits. Network speeds are quoted in bits per second, while file sizes are in bytes. A 100 Mbps connection moves at most 100 ÷ 8 = 12.5 megabytes each second, before overheads. A lower-case b means bits, and an upper-case B means bytes.

Practical tips

Use decimal figures when comparing products, since that is how they are sold.
Expect a formatted drive to show a lower figure on some systems, and a small further amount is used by file-system structures.
When a limit is stated, such as an upload cap, check whether it means MB or MiB.

The data storage converter supports both decimal and binary units.

Frequently asked questions

Is a kilobyte 1,000 or 1,024 bytes?: By the SI definition, 1,000. A kibibyte (KiB) is 1,024 bytes. In older usage, kilobyte was often used for 1,024.
Why do drive makers use decimal units?: They follow the SI prefixes, in which kilo means 1,000, and that makes the number on the box larger.
How do I convert Mbps to MB per second?: Divide by 8. 100 Mbps is 12.5 MB per second.

About the author

Editorial Team. The Editorial Team writes, checks and maintains every tool and guide on this site. The calculation logic behind the calculators is covered by automated tests, examples are worked out and re-checked before publishing, and pages are updated when we find a mistake or a rule changes. Corrections are welcome through the contact page.

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