IEC Prefixes

Introduction

In December 1998 the International Electrotechnical Commission (IEC), the leading international organization for worldwide standardization in electrotechnology, approved as an IEC International Standard names and symbols for prefixes for binary multiples for use in the fields of data processing and data transmission. The prefixes are as follows:

Specific units of IEC 60027-2 A.2 and ISO/IEC 80000
IEC prefix		Representations				Customary prefix
Name	Symbol	Base 2	Base 1024	Value	Base 10	Name	Symbol
kibi	Ki	2¹⁰	1024¹	1024	≈ 1.02×10³	kilo	k^[1] or K
mebi	Mi	2²⁰	1024²	1048576	≈ 1.05×10⁶	mega	M
gibi	Gi	2³⁰	1024³	1073741824	≈ 1.07×10⁹	giga	G
tebi	Ti	2⁴⁰	1024⁴	1099511627776	≈ 1.10×10¹²	tera	T
pebi	Pi	2⁵⁰	1024⁵	1125899906842624	≈ 1.13×10¹⁵	peta	P
exbi	Ei	2⁶⁰	1024⁶	1152921504606846976	≈ 1.15×10¹⁸	exa	E
zebi	Zi	2⁷⁰	1024⁷	1180591620717411303424	≈ 1.18×10²¹	zetta	Z
yobi	Yi	2⁸⁰	1024⁸	1208925819614629174706176	≈ 1.21×10²⁴	yotta	Y

It is suggested that in English, the first syllable of the name of the binary-multiple prefix should be pronounced in the same way as the first syllable of the name of the corresponding SI prefix, and that the second syllable should be pronounced as "bee."

It is important to recognize that the new prefixes for binary multiples are not part of the International System of Units (SI), the modern metric system. However, for ease of understanding and recall, they were derived from the SI prefixes for positive powers of ten. As can be seen from the above table, the name of each new prefix is derived from the name of the corresponding SI prefix by retaining the first two letters of the name of the SI prefix and adding the letters "bi," which recalls the word "binary." Similarly, the symbol of each new prefix is derived from the symbol of the corresponding SI prefix by adding the letter "i," which again recalls the word "binary."

¹For consistency with the other prefixes for binary multiples, the symbol Ki [uppercase "K"] is used for 2¹⁰ rather than ki [lowercase "k"].