Mega- (symbol M) is an SI prefix in the SI system of units denoting a factor of 10⁶, 1,000,000 (one million).

For example, 1 MW (megawatt) = 1,000,000 watts = 1,000 kilowatts.

Confirmed in 1960, it comes from the Greek μέγας, meaning great.

Other common examples of usage

• one megaton [of TNT] (a unit often used in measuring the explosive power of nuclear weapons) is 1,000,000 tons of TNT.
• megahertz—frequency of electromagnetic radiation for radio and television broadcasting, GSM, etc. 1 MHz = 1,000,000 Hz.

Square and cubic forms

As the SI-prefixes take precedence over exponents,

• 1 Mm² means one square megametre or the size of a square of 1,000,000 m × 1,000,000 m or $10^\{12\}$ m² (and not 1,000,000 × a square metre or $10^\{6\}$ m²)
• 1 Mm³ means one cubic megametre or the size of a cube of 1,000,000 m × 1,000,000 m × 1,000,000 m or $10^\{18\}$ m² (and not 1,000,000 × a cubic metre or $10^\{6\}$ m³)

Computing

In computing, mega- can sometimes denote 1,048,576 (2²⁰) of information units (example: a megabyte, a megaword), but can denote 1,000,000 (10⁶) of other quantities, for example, transfer rates: 1 megabit/s = 1,000,000 bit/s.

The prefix mebi- has been suggested as a prefix for 2²⁰ to avoid ambiguity, but is yet to be widely used.

See also

• SI prefix
• Binary prefix
• Mebibyte
• Orders of magnitude

References

External links

• BIPM website