Mega-

Mega is a unit prefix in metric systems of units denoting a factor of one million (10⁶ or 1000000). It has the unit symbol M. It was confirmed for use in the International System of Units (SI) in 1960. Mega comes from the Greek μέγας megas, meaning "great".^[1]

Common examples of usage

Megapixel: 1 million pixels in a digital camera
One megatonne of TNT equivalent amounts to approx. 4 petajoules and is the approximate energy released on igniting one million tonnes of TNT. The unit is often used in measuring the explosive power of nuclear weapons.
Megahertz: frequency of electromagnetic radiation for radio and television broadcasting, GSM, etc. 1 MHz = 1,000,000 Hz.
Megabyte: unit of information equal to- depending on definition- either one million bytes (SI standard) or 1048576 bytes (traditional).
Megawatt: equal to one million watts of power. It is commonly used to measure the output of power plants, as well as the power consumption of electric locomotives, data centers, and other entities that heavily consume electricity.

Exponentiation

When units occur in exponentiation, such as in square and cubic forms, any multiples-prefix is considered part of the unit, and thus included in the exponentiation.

1 Mm² means one square megametre or the size of a square of 1000000m by 1000000m or 10¹²m², and not 1000000square metres (10⁶ m²).
1 Mm³ means one cubic megametre or the size of a cube of 1000000m by 1000000m by 1000000m or 10¹⁸ m³, and not 1000000cubic metres (10⁶ m³)

Computing

In some fields of computing, mega may sometimes denote 1,048,576 (2²⁰) of information units, for example, a megabyte, a megaword, but denotes 1000000 (10⁶) units of other quantities, for example, transfer rates: 1megabit/s = 1000000bit/s. The prefix mebi- has been suggested as a prefix for 2²⁰ to avoid ambiguity.

SI prefixes

Prefix		Base 1000	Base 10	Decimal	English word		Adoption^{[nb 1]}
Name	Symbol	Base 1000	Base 10	Decimal	Short scale	Long scale	Adoption^{[nb 1]}
yotta	Y	1000⁸	10²⁴	1000000000000000000000000	septillion	quadrillion	1991
zetta	Z	1000⁷	10²¹	1000000000000000000000	sextillion	trilliard	1991
exa	E	1000⁶	10¹⁸	1000000000000000000	quintillion	trillion	1975
peta	P	1000⁵	10¹⁵	1000000000000000	quadrillion	billiard	1975
tera	T	1000⁴	10¹²	1000000000000	trillion	billion	1960
giga	G	1000³	10⁹	1000000000	billion	milliard	1960
mega	M	1000²	10⁶	1000000	million		1873
kilo	k	1000¹	10³	1000	thousand		1795
hecto	h	1000^2/3	10²	100	hundred		1795
deca	da	1000^1/3	10¹	10	ten		1795
		1000⁰	10⁰	1	one		–
deci	d	1000^−1/3	10⁻¹	0.1	tenth		1795
centi	c	1000^−2/3	10⁻²	0.01	hundredth		1795
milli	m	1000⁻¹	10⁻³	0.001	thousandth		1795
micro	µ	1000⁻²	10⁻⁶	0.000001	millionth		1873
nano	n	1000⁻³	10⁻⁹	0.000000001	billionth	milliardth	1960
pico	p	1000⁻⁴	10⁻¹²	0.000000000001	trillionth	billionth	1960
femto	f	1000⁻⁵	10⁻¹⁵	0.000000000000001	quadrillionth	billiardth	1964
atto	a	1000⁻⁶	10⁻¹⁸	0.000000000000000001	quintillionth	trillionth	1964
zepto	z	1000⁻⁷	10⁻²¹	0.000000000000000000001	sextillionth	trilliardth	1991
yocto	y	1000⁻⁸	10⁻²⁴	0.000000000000000000000001	septillionth	quadrillionth	1991

↑ Prefixes adopted before 1960 already existed before SI. 1873 was the introduction of the CGS system.

References

↑ "Oxford English Dictionary (OED Online)". www.oed.com (3rd ed.). Oxford University Press. June 2001. Retrieved 2017-09-18. (Subscription required (help)). Origin: A borrowing from Greek. Etymon: Greek μεγα-. ... Forming scientific and technical terms with the sense ‘very large’, ‘comparatively large’, or (esp. in Pathol.) ‘abnormally large’, often having correlatives beginning micro-, and sometimes also synonyms beginning macro-.

External links

BIPM website

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[2] Prefixes adopted before 1960 already existed before SI. 1873 was the introduction of the CGS system.

[1] "Oxford English Dictionary (OED Online)". www.oed.com (3rd ed.). Oxford University Press. June 2001. Retrieved 2017-09-18. (Subscription required (help)). Origin: A borrowing from Greek. Etymon: Greek μεγα-. ... Forming scientific and technical terms with the sense ‘very large’, ‘comparatively large’, or (esp. in Pathol.) ‘abnormally large’, often having correlatives beginning micro-, and sometimes also synonyms beginning macro-.