By a curious historical confusion, two different systems for naming large numbers exist, one in the US and the other in Britain and other parts of the English-speaking world. This could be troublesome, but these days such large numbers are much more often given in unambiguous scientific notation, and the US usage is in any case coming to dominate, as it has almost completely with billion.
The original scheme, invented in France in the sixteenth century, started with million and multiplied 1 by that number the required number of times. The name of the unit was then based on the number of multiplications, using Latin numerals. So a sextillion was 1 multiplied by a million six times, making a number expressed by 1 followed by 36 zeroes (1036 in scientific notation).
In the eighteenth century French mathematicians changed to multiples of a thousand instead, but took over the existing number names; the Latin numbers then marked one less than the number of multiplications, so that trillion was 1 multiplied by a thousand four times. The US system was based on the thousands scheme, but the British stayed with the older millions one.
The following table gives some names and values in the two systems:
Number
word
Millions
scheme
Thousands
scheme
million
106
106
billion (Latin bi-, twice)
1012
109
trillion (Latin tres, three)
1018
1012
quadrillion (Latin quattour, four)
1024
1015
quintillion (Latin quinque, five)
1030
1018
sextillion (Latin sex, six)
1036
1021
septillion (Latin septem, seven)
1042
1024
octillion (Latin octo, eight)
1048
1027
nonillion (Latin nonus, ninth)
1054
1030
decillion (Latin decem, ten)
1060
1033
Two parallel sets of prefixes for number multiples exist, one derived from Latin, the other from Greek. These appear widely in compounds but are no longer much used to create new words, the job having been largely passed to the SI method described below, especially in scientific usage.
Number
Latin
Greek
The standard system of prefixes for multiples these days is that laid down in SI units (Système International D’Unités), an international agreement dating from 1960, which defines standard units for quantities and the names for the decimal prefixes to use with them. These are widely used.
The standard SI prefixes for multiples are:
yotta-
1024
Based on Latin octo‑, eight
ronna-
1027
Loosely based on Greek ennéa, nine
quetta-
1030
Loosely based on Latin decem, ten
The standard SI prefixes for fractional quantities are:
ronto-
10-27
Loosely based on Greek ennéa, nine
quecto-
10-30
Loosely based on Latin decem, ten
The prefixes hecto-, deca-, deci-, and centi- are generally avoided in scientific work.
The use of decimal prefixes to describe the similar — but not identical — binary multiples used in computing (such as megabyte or terabit) has caused confusion — as a result of various conventions, a megabyte can be 1,048,576 or 1,024,000 or 1,000,000.
In 1998 the International Electrotechnical Commission (IEC) agreed an international standard for a new group of prefixes that removes the ambiguity; names use the first two letters of the SI decimal prefix, followed by the letters bi, for binary. These are only slowly coming into use.
kibi-
210
mebi-
220
gibi-
230
tebi-
240
pebi-
250
exbi-
260
zebi-
270
yobi-
280
Copyright © Michael Quinion 2008–. All rights reserved. Last updated 10 Jan 2024. Your comments are very welcome.