Prefixes - AMA Manual of Style

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Prefixes 

Prefixes

Chapter:
Units of Measure
Author(s):

Phil B. Fontanarosa

and Stacy Christiansen

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Prefixes

Prefixes are combined with base units and derived units to form multiples of SI units. The factors designated by prefixes are powers of 10, and most prefixes involve exponents that are simple multiples of 3, thereby facilitating conversion procedures using successive multiplications by 103 or 10−3.

Factor

Prefix

Symbol

1024

yotta

Y

1021

zetta

Z

1018

exa

E

1015

peta

P

1012

tera

T

109

giga

G

106

mega

M

103

kilo

k

102

hecto

h

101

deka (deca)

da

10−1

deci

d

10−2

centi

c

10−3

milli

m

10−6

micro

μ

10−9

nano

n

10−12

pico

p

10−15

femto

f

10−18

atto

a

10−21

zepto

z

10−24

yocto

y

Compound prefixes formed by the combination of 2 or more SI prefixes generally are not used. It is preferable to use an expression with a single prefix.

Preferred:

nm (nanometer)

Avoid:

mμm (millimicrometer)

The kilogram is the only SI base unit with a prefix as part of its name and symbol (kg). However, because compound prefixes are not recommended, prefixes relating to mass are combined with gram (g) rather than kilogram (kg).

Preferred:

mg (milligram)

Avoid:

μkg (microkilogram)

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