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Prefixes (milli, kilo, mega)
Beginner
Powers of ten shorthand for very large or small values.
k=10³, m=10⁻³, μ=10⁻⁶Prefixes are powers of ten attached to units so numbers stay readable: nano 10⁻⁹, micro 10⁻⁶, milli 10⁻³, kilo 10³, mega 10⁶, giga 10⁹. They change the size of the unit, not the physical quantity.
A 2.5 GHz processor runs at 2.5×10⁹ cycles per second. A 450 nm light wave has wavelength 4.5×10⁻⁷ m.
Squares and cubes of prefixed units multiply the factor: 1 cm² = 10⁻⁴ m², not 10⁻² m².
In more detail
Prefixes such as kilo, milli and micro are powers of ten placed before a unit. They let us write very large or very small quantities without long strings of zeros.
Real-world uses
- Electronics labels use nanofarads and kilohms to keep component values short and readable.
- Data storage sizes such as gigabytes use prefixes that scale by powers of ten.
- Computer memory is quoted in kilobytes, megabytes and gigabytes, and the same prefixes are used in physics for wavelengths, currents and frequencies.
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Frequently asked questions
What does the prefix k stand for?
Kilo means one thousand, so one kilometre is 1000 metres.
Is a millisecond one-thousandth of a second?
Yes. The prefix milli means 10 to the power minus 3, so a millisecond is 0.001 s.
Why does the prefix matter in a calculation?
A prefix changes the value by a power of ten. Forgetting to convert 5 mA to 0.005 A makes a result a thousand times too large.
Related topics in Measurement & Math Tools
Physical quantity · SI base units · Derived units · Scientific notation · Length measurement · Vernier calliper