Appendix A: Symbols and Prefixes

(Appendix A last revised March 2013)

This appendix of the Author's Kit provides recommendations on prefixes, unit symbols and abbreviations, acronyms, and factors for conversion into units of the International System.

Prefixes

Recommended prefixes indicating decimal multiples or submultiples of units and their symbols are as follows: 

Multiple Prefix Abbreviation
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
10 deka 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

Avoid using compound prefixes, such as micromicro for pico and kilomega for giga. The abbreviation of a prefix is considered to be combined with the abbreviation/symbol to which it is directly attached, forming with it a new unit symbol, which can be raised to a positive or negative power and which can be combined with other unit abbreviations/symbols to form abbreviations/symbols for compound units. For example:

1 cm3 = (10-2 m)3 = 10-6 m3
1 μs-1 = (10-6 s)-1 = 106 s-1
1 mm2/s = (10-3 m)2/s = 10-6 m2/s

Abbreviations and Symbols

Whenever possible, avoid using abbreviations and symbols in paragraph text; however, when it is deemed necessary to use such, define all but the most common at first use. The following is a recommended list of abbreviations/symbols for some important units, and it also includes other common abbreviations and go site acronyms that may be used in tables and figures, and, if deemed necessary, in paragraph text. The form of unit abbreviations/symbols is the same for both singular and plural usage, and they are not followed by a period. The distinction between uppercase and lowercase letters should be carefully observed. When a compound unit is formed by the multiplication of two or more units, its abbreviation/symbol consists of the symbols for the separate units joined by a raised dot, for example, N·m for newton-meter. When a compound unit is formed by division of one unit by another, its abbreviation/symbol consists of the symbols for the separate symbols either separated by solidus (slant) or multiplied using negative powers, for example, m/s or m·s-1 for meters per second.

 

alternating current ac
American wire gauge AWG
ampere A
ampere-hour Ah
ampere-turn At
amplitude modulation AM
antilogarithm antilog
atomic mass unit (unified) U
audio frequency AF
automatic frequency control AFC
automatic gain control AGC
automatic volume control AVC
average avg
backward-wave oscillator BWO
bar bar
barn b
beat-frequency oscillator BFO
bel B
billion electronvolts GeV
binary coded decimal BCD
British thermal unit Btu
calorie cal
calorie (International Table calorie) calIT
calorie (thermochemical calorie) calth
candela cd
candela per square foot cd/ft2
candela per square meter cd/m2
cathode-ray oscilloscope CRO
cathode-ray tube CRT
centimeter cm
centimeter-gram-second CGS
circular mil cmil
continuous wave CW
coulomb C
coupling capacitor voltage transformer ccvt
cubic centimeter cm3
cubic foot ft3
cubic foot per minute ft3/min
cubic foot per second ft3/s
cubic inch in3
cubic meter m3
cubic meter per second m3/s
cubic yard yd3
curie Ci
current transformer Ct
decibel dB
decibel referred to one milliwatt dBm
degree (temperature) Celsius °C
degree (temperature) Fahrenheit °F
diameter dia
direct current dc
double sideband DSB
electrocardiograph ECG
electroencephalograph EEG
electromagnetic compatibility EMC
electromagnetic unit EMU
electromotive force EMF
electronic data processing EDP
electronvolt eV
electrostatic unit ESU
extra high voltage EHV
extremely high frequency EHF
extremely low frequency ELF
farad F
field-effect transistor FET
foot ft
footcandle fc
footlambert fL
foot per minute ft/min
foot per second ft/s
foot per second squared ft/s2
foot poundal ft·pdl
foot pound-force ft·lbf
frequency modulation FM
frequency-shift keying FSK
gal Gal
gigaelectronvolt GeV
gigahertz GHz
gram g
henry H
hertz Hz
high frequency HF
high voltage HV
horsepower hp
hour h
inch in
inch per second in/s
inductance-capacitance LC
infrared IR
inside diameter ID
intermediate frequency IF
joule J
joule per kelvin J/K
kelvin K
kiloelectronvolt keV
kilogram kg
kilohertz kHz
kilohm
kilojoule kJ
kilometer km
kilometer per hour km/h
kilovar kvar
kilovolt kV
kilovoltampere kVA
kilowatt kW
kilowatthour kWh
knot knot
liter L
liter per second L/s
logarithm log
logarithm, natural ln
low frequency LF
lumen lm
lumen per square foot lm/ft2
lumen per square meter lm/m2
lumen per watt lm/W
lumen second lm·s
lux lx
magnetohydrodynamics MHD
magnetomotive force MMF
medium frequency MF
megaelectronvolt MeV
megahertz MHz
megavolt MV
megavar Mvar
megawatt MW
megohm
metal-oxide semiconductor MOS
meter m
meter-kilogram-second MKS
mho mho
microampere μA
microbar μbar
microfarad μF
microgram μg
microhenry μH
micrometer μm
micrombo μmho
micron μm
microsecond μs
microsiemens μS
microwatt μW
mil mil
mile per hour mi/h
mile (statute) mi
milliampere mA
millibar mbar
millibarn mb
milligram mg
millihenry mH
milliliter mL
millimeter mm
millimeter of mercury, conventional mmHg
millisecond ms
millisiemens mS
millivolt mV
milliwatt mW
minute (time) min
nanoampere nA
nanofarad nF
nanometer nm
nanosecond ns
nanowatt nW
nautical mile nmi
neper Np
newton N
newton meter Nm
newton per square meter N/m2
ohm Ω
ounce (avoirdupois) oz
outside diameter OD
pascal Pa
per unit pu
phase modulation PM
picoampere pA
picocoloumb pC
picofarad pF
picosecond ps
picowatt pW
pint pt
pound lb
poundal pdl
pound-force lbf
pound-force foot lbf·ft
pound-force per square inch lbf/in2
pound (force) per square inch lbf/in2
power factor PF
private branch exchange PBX
pulse-amplitude modulation PAM
pulse-code modulation PCM
pulse-count modulation PCM
pulse-duration modulation PDM
pulse-position modulation PPM
pulse-repetition frequency PRF
pulse-repetition rate PRR
pulse-time modulation PTM
pulse-width modulation PWM
quart qt
rad rd
radian rad
radio frequency RF
radio-frequency interference RFI
rem rem
resistance-capacitance RC
resistance-inductance-capacitance RLC
revolution per minute r/min
revolution per second r/s
roentgen R
root-mean-square rms
second (time) s
short wave SW
siemens S
signal-to-noise ratio SNR
semiconductor controlled rectifier SCR
silicon controlled rectifier SCR
single sideband SSB
square foot ft2
square inch in2
square meter m2
square yard yd2
standing-wave ratio SWR
steradian sr
superhigh frequency SHF
television TV
television interference TVI
tesla T
thin-film transistor TFT
ton, short ton
ton, metric ton
transverse electric TE
transverse electromagnetic TEM
transverse magnetic TM
traveling-wave tube TWT
ultrahigh frequency UHF
ultraviolet UV
(unified) atomic mass unit u
vacuum-tube voltmeter VTVM
var var
variable-frequency oscillator VFO
very high frequency VHF
very low frequency VLF
vestigial sideband VSB
volt V
voltage controlled oscillator VCO
voltage standing-wave ratio VSWR
voltage transformer vt
voltampere VA
volume unit vu
watt W
watthour Wh
watt per steradian W/sr
watt per steradian square meter W/(sr m2)
weber Wb
yard yd
Conversion Factors

The following are some factors for conversion into units of the International System.

Length
1 inch = 2.54 centimeters (exactly)
1 foot = 0.3048 meter (exactly)
1 mile = 1609.3 meters
1 nautical mile = 1852 meters (exactly)
1 micron = 1 micrometer (exactly)
1 angstom = 0.1 nanometer (exactly)

Area
1 square inch = 6.4516 square centimeters (exactly)
1 square foot = 0.092 903 square meter
1 circular mil = 5.0671 x 10-4 square millimeter
1 acre = 4046.9 square meters
1 barn = 10-28 square meter (exactly)
1 hectare = 10 000 square meters (exactly)

Volume
1 cubic inch = 16.387 cubic centimeters
1 cubic foot = 0.028 317 cubic meter
1 fluid ounce (UK) = 28.413 cubic centimeters
1 fluid ounce (US) = 29.574 cubic centimeters
1 gallon (UK) = 4546.1 cubic centimeters
1 gallon (US) = 3785.4 cubic centimeters
1 barrel (US) (for petroleum; etc) = 0.158 99 cubic meter
1 acre foot = 1233.5 cubic meters
1 liter = 1000 cubic centimeters (exactly)

Speed
1 foot per minute = 5.08 millimeters per second (exactly)
1 mile per hour = 0.44704 meter per second (exactly)
1 knot = 0.514 44 meter per second
1 kilometer per hour = 0.277 78 meter per second

Mass
1 ounce (avoirdupois) = 28.350 grams
1 pound = 0.453 59 kilogram
1 slug = 14.594 kilograms
1 short ton = 907.18 kilograms
1 long ton = 1016.0 kilograms
1 tonne = 1000 kilograms (exactly)

Density
1 pound per cubic foot = 16.018 kilograms per cubic meter
1 pound per cubic inch = 27 680 kilograms per cubic meter

Force
1 poundal = 0.138 25 newton
1 ounce-force = 0.278 01 newton
1 pound-force = 4.4482 newtons
1 kilogram-force = 9.806 65 newtons (exactly)
1 dyne = 10-5 newton (exactly)

Pressure
1 poundal per square foot = 1.4882 pascals (newtons per square meter)
1 pound-force per square foot = 47.880 pascals
1 pound-force per square inch = 6894.8 pascals
1 conventional foot of water = 2989.1 pascals
1 conventional millimeter of mercury = 133.32 pascals
1 torr = 133.32 pascals
1 standard atmosphere (760 torr) = 101 325 pascals (exactly)
1 technical atmosphere (1 kgf/cm2) = 98 066.5 pascals (exactly)
1 bar = 100 000 pascals (exactly)

Energy, Work
1 foot poundal = 0.042 140 joule
1 foot pound-force = 1.3558 joules
1 British thermal unit (thermochemical) = 1054 joules
1 British thermal unit (International Table) = 1055 joules
1 calorie (thermochemical) = 4.184 joules (exactly)
1 calorie (International Table) = 4.1868 joules (exactly)
1 electronvolt = 1.602 x 10-19 joule
1 erg = 10-7 joule (exactly)

Power
1 foot pound-force per second = 1.3558 watts
1 horsepower (metric) = 735.50 watts
1 horsepower (British) = 745.70 watts
1 horsepower (electrical) = 746 watts (exactly)
1 British thermal unit (International Table) per hour = 0.2931 watt
1 erg per second = 10-7 watt (exactly)

Quantities of Light
1 footcandle = 10.764 lux (lumens per square meter)
1 footlambert = 3.4263 candelas per square meter

Quantities of Electricity and Magnetism
1 ESU of current ≃ 3.3356 x 10-10 ampere
1 EMU of current = 10 amperes (exactly)
1 ESU of electric potential ≃ 299.79 volts
1 EMU of electric potential = 10-8 volt (exactly)
1 ESU of capacitance ≃ 1.1126 x 10-12 farad
1 EMU of capacitance = 109 farads (exactly)
1 ESU of inductance ≃ 8.9876 x 1011 henrys
1 EMU of inductance = 10-9 henry (exactly)
1 ESU of resistance ≃ 8.9876 x 1011 ohms
1 EMU of resistance = 10-9 ohm (exactly)
1 gilbert ≃ 0.795 77 ampere
1 oersted ≃ 79.577 amperes per meter
1 maxwell = 10-8 weber (exactly)
1 gauss = 10-4 tesla (exactly)

Note that ESU means electrostatic CGS unit; EMU means electromagnetic CGS unit. In this list, the sign ≃ is to be read “corresponds to.” Since the change from either CGS system to the International System of Units involves a change in quantities, conversion of units by multiplication by a pure number is not, strictly speaking, possible. However, a physical situation which can be described as a “current” of 1 abampere can also be described as a current of 10 amperes.