Byte Unit Converter (KB vs KiB, MB vs MiB)

Understanding the byte unit converter — concept and principle

Storage sizes are written with two different systems of prefixes. Decimal (SI) prefixes use powers of 1000: kB, MB, GB, TB. Binary (IEC) prefixes use powers of 1024: KiB, MiB, GiB, TiB. Drive makers and network speeds use the decimal system, while memory chips and many operating systems count in binary, often still labelled "GB". This converter turns a value in any of these units into bytes, GB, GiB, TB and TiB, so you can see why a new "1 TB" drive shows up as about 931 GB on a computer.

A GiB is 7.4% bigger than a GB, so the same bytes make fewer GiB.

How it is calculated

Bytes = value × unit size, where 1 kB = 10³, 1 MB = 10⁶, 1 GB = 10⁹, 1 TB = 10¹² bytes and 1 KiB = 2¹⁰ = 1024, 1 MiB = 2²⁰ = 1,048,576, 1 GiB = 2³⁰ = 1,073,741,824, 1 TiB = 2⁴⁰ = 1,099,511,627,776 bytes.
Each output = bytes ÷ the size of the target unit.

The principle

Computers address memory in powers of two, so early engineers borrowed "kilo" for 1024 because it was close to 1000. The gap grows with every step: 2.4% at kilo, 4.9% at mega, 7.4% at giga and 10% at tera. To remove the ambiguity, the IEC introduced the binary prefixes kibi, mebi, gibi and tebi in 1998, leaving kilo, mega and giga with their SI meanings. Both systems describe the same number of bytes; only the unit is different, like measuring a distance in miles or kilometres.

Worked example

Input: 1 TB.
Bytes: 1 × 10¹² = 1,000,000,000,000.
GB (10⁹): 10¹² ÷ 10⁹ = 1,000.
GiB (2³⁰): 10¹² ÷ 1,073,741,824 = 931.3225746.
TB: 1. TiB (2⁴⁰): 10¹² ÷ 1,099,511,627,776 = 0.9094947018.

Each point is the calculator re-run with only “Value” changed; the gold point is the default example. Change the inputs above and this chart follows your numbers.

Value	Bytes
0.25	250,000,000,000
0.5	500,000,000,000
0.75	750,000,000,000
1	1,000,000,000,000
1.25	1,250,000,000,000
1.5	1,500,000,000,000
2	2,000,000,000,000

How to read the result

The ratio TB ÷ TiB is about 0.909, so a drive's capacity in TiB is roughly 9% smaller than the number on the box, and no space is actually missing. Windows File Explorer reports binary values with GB labels, while macOS (since version 10.6) and most drive packaging use decimal units. The real usable space is smaller again, because the file system, partitions and recovery areas take some room.

Common mistakes

Treating kB and KiB as equal for large files; the difference reaches 10% at terabyte scale.
Confusing bytes (B) with bits (b): a 100 Mb/s connection moves at most 12.5 MB/s.
Writing "KB" and assuming everyone reads it the same way; the SI symbol is lower-case kB, and KiB is unambiguous.

Keep in mind: Advertised capacity is the raw decimal size. Formatting overhead, reserved space and file-system metadata reduce what you can store, and these vary by device and system.

Frequently asked questions

Why does my 1 TB drive show 931 GB?

The drive has 10¹² bytes, which is 931 GiB; the operating system labels that as GB.

Is RAM sold in GB or GiB?

Memory modules come in binary sizes, so "16 GB" of RAM is 16 GiB, or 17,179,869,184 bytes.

How many MB are in a GB?

1000 in SI units, and 1024 MiB in a GiB.

Sources: IEC 80000-13, Quantities and units — Part 13: Information science and technology · BIPM, The International System of Units (SI Brochure), 9th edition, 2019

Checked 8 Nov 2026. Standard formulas and RFC/IEEE definitions, computed locally in your browser — nothing you type is sent anywhere.

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