Guide

Comparing data volumes

Storage plans, upload limits and drive sizes are only comparable when the same prefix logic is used.

Keeping decimal and binary apart

Kilobyte, megabyte, gigabyte and terabyte are decimal prefixes based on powers of ten. Kibibyte, mebibyte, gibibyte and tebibyte are binary prefixes based on powers of two. The IEC introduced the second notation in 1998 to end exactly this confusion. Both systems are valid but must not be mixed.

The deviation grows with every step

Between KiB and kB the difference is 2.4 %. For MiB against MB it is 4.9 %, for GiB against GB 7.4 %, for TiB against TB 10.0 % and for PiB against PB 12.6 %. The reason is that 1024 against 1000 multiplies again at every step, which makes the percentage difference grow.

Bits per second and bytes per second

Transmission rates add a second factor: bit against byte. A figure in Mbit/s is a factor of eight above the same figure in MB/s. When comparing a provider's upload limit against a file size, first convert the rate to bytes and only then determine the time.

What drive figures mean

Manufacturer figures on drives and storage media are decimal because that yields larger numbers. Operating systems display binary because memory is technically organised in powers of two. A drive sold as 1 TB therefore appears in the system as about 931 GiB. That is not a defect but the same amount in a different unit.

Matching conversions

Gigabyte to GibibyteGB → GiBData Gibibyte to GigabyteGiB → GBData Kilobyte to KibibyteKB → KiBData Megabyte to GigabyteMB → GBData Gigabyte to TerabyteGB → TBData Petabyte to GigabytePB → GBData

Matching tables

TableData volumes: binary versus decimal TableBandwidth: Mbit/s in MB/s

Unit family: Data

Common questions

How many MB are in a GB?

In decimal arithmetic 1000 MB. In binary arithmetic 1 GiB is exactly 1024 MiB.

Why does my system show less storage?

Manufacturers count in decimal, operating systems in binary. At 1 TB the deviation is about 7.4 %.

What does the i in MiB mean?

It marks the binary prefix per IEC 80000-13: MiB stands for 2²⁰ bytes, MB for 10⁶ bytes.

Is a terabyte more than a tebibyte?

Yes, 1 TB is 10¹² bytes, 1 TiB is 1099511627776 bytes, so about 10 % more.

Sources

IEC 80000-13Binary prefixes KiB, MiB, GiB, TiB against the decimal SI prefixes.BIPM SI BrochureSI base units, prefixes and official SI context.

When not to use

Do not use as the sole basis for official, medical, safety-critical or contractual decisions.

Citation

Citation note: UnitCloud, guide, sources reviewed: September 2026. Source basis: IEC 80000-13 · BIPM SI Brochure.