Measurement Units and Abbreviations

This chapter provides guidelines for units of measure and also lists abbreviations and symbols for frequently used units.

General Rules for Using Units of Measure

Follow these guidelines:

1. When to abbreviate units and when to spell out units as words

• Abbreviate units when you report a numerical value, e.g., “The ESP32 Wi-Fi/BT firmware can only support 40 MHz crystal oscillator for now.”

• Always spell out a unit of measure as a word if a numeral does not precede it, e.g., “The default baud rate for ESP8266 is 115200.”

• When starting a sentence with a number and unit, both must be spelled out as words, e.g., “One thousand six hundred and eighty-seven kilograms of ground beef were randomly sampled and tested for E. coli contaminants between August 21 and November 21, 1995.”

Even if a sentence starts with a spelled-out number and unit, use numerals when appropriate in the rest of the sentence, e.g., “One thousand six hundred and eighty-seven kilograms of ground beef were randomly sampled, resulting in 2.5 kg of samples. Then the samples were tested for E. coli contaminants between August 21 and November 21, 1995.”

You can avoid spelling out number and unit by restructuring a sentence, e.g., “The ground beef in the amount of 1687 kg was randomly sampled and tested for E. coli contaminants between August 21 and November 21, 1995.”

2. When to hyphenate:

• When you use a spelled-out unit of measure in a compound adjective, hyphenate the compound, e.g., 17-inch display, 3-meter cable.

• When you use an abbreviated unit in a compound adjective, do not hyphenate it; add a space between the number and the abbreviation. E.g., 20 nA battery, 30 GB capacity.

3. Unless otherwise noted, singular and plural units are abbreviated the same.

• One kilogram and 10 kilograms are abbreviated as 1 kg and 10 kg.

4. Capitalization: With the exception of degrees Celsius, Fahrenheit, and Rankine, units of measure derived from a proper name are not capitalized when spelled out, but their unit symbols are capitalized. E.g., the unit symbol for joule is J.

5. Mixing spelled-out units and their abbreviations: Do not mix spelled-out units and their abbreviations in complex units of measure. Either spell out complex units or use their abbreviation (m/s, Bd/s).

Example

Preferred	Avoid
meters per second or m/s	m/second
baud per second or Bd/s	Baud/s

• Do not mix a spelled-out prefix with an abbreviated unit or an abbreviated prefix with a spelled-out unit.

Example

Preferred	Avoid
kHz	kiloHz, khertz

Prefixes for Units of Measure

Prefixes for Units of Measure

Factor	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
101	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

Frequently Used Units of Measure

Frequently Used Units of Measure

Factor	Prefix	Abbreviation
ampere	electric current	A
ampere-hour	electric charge, derivative of coulomb	Ah
amperes per meter	magnetic field strength	A/m
amperes per square meter	current density	A/m2
baud	the speed at which information is sent	Bd
bit	the most basic unit of information that can be stored in a computer	bit
bits per second	speed of data transmission	bit/s
byte	a basic unit for storing computer information, used for measuring the size of a document. A byte is usually made of eight bits	B
centimeter	length	cm
characters per inch	letter spacing in typography	cpi
characters per second	digital data transfer rate	cps
coulomb	electric charge	C
decibel	sound intensity	dB
degree	angular measure	°
degree Celsius	temperature	°C
degree Fahrenheit	temperature	°F
dots per inch	the ability of a computer screen or printer to produce a clear image/resolution	dpi
exabyte	a unit for measuring computer information, equal to 1024 PB	EB
Farad	capacitance	F
gigabit	a unit of information equal to 1024 Mbit	Gbit
gigabit per second	speed of data transmission	Gbps
gigabyte	a unit for measuring computer information, equal to 1024 MB	GB
gigahertz	a unit for measuring the frequency of sound waves, radio waves, and computer clock signals, equal to 1000 MHz	GHz
gilbert	magnetomotive force	Gb
gram	mass, weight	g
henry	inductance	H
hertz	a unit for measuring the frequency of sound waves, radio waves, and computer clock signals	Hz
joule	energy	J
kilobits per second	the speed of a modem	Kbps
kilobyte	a unit for measuring computer information, containing 1024 bytes	KB
kilohertz	frequency	kHz
kiloohm	electric resistance	kΩ, kiloohm
kilometer	length	km
kilowatt	power	kW
kilowatt-hour	energy (usually electric power consumption)	kWh
megabit	a unit of information equal to 1024 Kbit	Mbit
megabits per second	speed of data transmission	Mbit/s
megabyte	a unit for measuring computer information, equal to 1024 KB	MB
megahertz	a unit for measuring the frequency of sound waves, radio waves, and computer clock signals, equal to 1000 kHz	MHz
meter	length	m
millimeter	length	mm
million instructions per second	computer speed	mips
ohm	electric resistance	Ω
petabyte	a unit for measuring computer information, equal to 1024 TB	PB
second	a unit of time	s
terabyte	a unit for measuring computer information, equal to 1024 GB	TB
tesla	magnetic flux density	T
volt	electric potential difference, electromotive force	V
watt	power	W
watt-hour	energy	Wh
yottabyte	a unit for measuring computer information, equal to 1024 ZB	YB
zettabyte	a unit for measuring computer information, equal to 1024 EB	ZB

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