Mega-

For other uses, see Mega (disambiguation).

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 Ancient Greek: μέγας, romanized: mégas, lit. 'great'.

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 one million bytes (SI standard).
• 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.
• Megadeath: (or megacorpse) is one million human deaths, usually used in reference to projected number of deaths from a nuclear explosion. The term was used by scientists and thinkers who strategized likely outcomes of all-out nuclear warfare.

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 10	Decimal	English word		Adoption	Etymology
Name	Symbol			Short scale	Long scale		Language	Source word
yotta	Y	1024	1000000000000000000000000	septillion	quadrillion	1991	Latin	eight
zetta	Z	1021	1000000000000000000000	sextillion	trilliard	1991	Latin	seven
exa	E	1018	1000000000000000000	quintillion	trillion	1975	Greek	six
peta	P	1015	1000000000000000	quadrillion	billiard	1975	Greek	five
tera	T	1012	1000000000000	trillion	billion	1960	Greek	four, monster
giga	G	109	1000000000	billion	milliard	1960	Greek	giant
mega	M	106	1000000	million		1873	Greek	great
kilo	k	103	1000	thousand		1795	Greek	thousand
hecto	h	102	100	hundred		1795	Greek	hundred
deca	da	101	10	ten		1795	Greek	ten
		100	1	one		–
deci	d	10−1	0.1	tenth		1795	Latin	ten
centi	c	10−2	0.01	hundredth		1795	Latin	hundred
milli	m	10−3	0.001	thousandth		1795	Latin	thousand
micro	μ	10−6	0.000001	millionth		1873	Greek	small
nano	n	10−9	0.000000001	billionth	milliardth	1960	Greek	dwarf
pico	p	10−12	0.000000000001	trillionth	billionth	1960	Spanish	peak, a little bit
femto	f	10−15	0.000000000000001	quadrillionth	billiardth	1964	Danish	fifteen, Fermi
atto	a	10−18	0.000000000000000001	quintillionth	trillionth	1964	Danish	eighteen
zepto	z	10−21	0.000000000000000000001	sextillionth	trilliardth	1991	Latin	seven
yocto	y	10−24	0.000000000000000000000001	septillionth	quadrillionth	1991	Latin	eight

See also

• Binary prefix
• Mebibyte
• Order of magnitude
• RKM code

External links

• BIPM website