So far we have just been considering pure numerical values, however in science and engineering we are most often dealing with measured quantities, e.g. metres (m), Volts (V), Newtons (N) etc.

Therefore using scientific notation we could have values like.

- 2 x 10
^{3}m . - 5 x 10
^{-3}V . - 2.5 x 10
^{4}N .

Some powers of 10 have there own symbol, e.g. k (kilo) is equivalent to ( x 10^{3}) . These are called decimal prefixes.
In engineering notation we write decimal prefixes before the units in place of the power of ten. e.g. Rather than 2 x 10^{3} m,
we would write 2 km (2 kilometres). The table below shows decimal prefixes for powers ranging from 10^{-12} to 10^{12} .

Power of 10 |
Decimal prefix |
Symbol |
---|---|---|

10^{12} |
Terra | T |

10^{9} |
Giga | G |

10^{6} |
Mega | M |

10^{3} |
kilo | k |

10^{-2} |
centi | c |

10^{-3} |
milli | m |

10^{-6} |
micro | µ |

10^{-9} |
nano | m |

10^{-12} |
pico | p |

Note there isn't a corresponding decimal prefix for every power of 10. So for some numbers we must first move the decimal point and adjust
the power of 10, until it matches one of the decimal prefixes.

e.g. 2 x 10^{4}m, is the same as 20 x 10^{3}m and therefore can be written as 20km.

Therefore unlike scientific notation, with engineering notation there can be more than one digit in front of the decimal point. However, there should be at least one digit in front of the decimal point and no more than three. So while values such as 0.1MV and 2000kA are not strictly speaking incorrect, it is more conventional to express these as, 100kV and 2MA respectively.