System International (SI) Notation

Article : Andy Collinson

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Overview:

Many of the schematics on this site have parts that are labeled using the System International (SI) notation system. The SI system is an easy way to describe values without the need for a decimal point. Circuits that have been previously drafted on paper may have a decimal point that has faded or hard to see. The SI system thereby overcomes this problem and offers a clear advantage. Multipliers are used in the SI system, taking the place of the decimal point in the conventional naming system.

Email :

Overview:

Many of the schematics on this site have parts that are labeled using the System International (SI) notation system. The SI system is an easy way to describe values without the need for a decimal point. Circuits that have been previously drafted on paper may have a decimal point that has faded or hard to see. The SI system thereby overcomes this problem and offers a clear advantage. Multipliers are used in the SI system, taking the place of the decimal point in the conventional naming system.

The following table indicates the multipliers for the commonest values used in electronics:-

Table of Multipliers

Using SI notation the unit of measurement appears at the end of the value. Resistor values are in ohms (R), capacitance is
measured in farads (F) and inductors are measured in Henrys (H). So a 10 ohm resistor would be wrote as
10R and a 4.7mH inductor 4m7H. Usually the end letter is omitted. More examples:-Number | Prefix | Symbol |

10 ^{12} | tera | T |

10 ^{9} | giga | G |

10 ^{6} | mega | M |

10 ^{3} | kilo | k |

10 ^{-3} | milli | m |

10 ^{-6} | micro | u |

10 ^{-9} | nano | n |

10 ^{-12} | pico | p |

2.2k = 2k2

4.7k = 4k7

2.5A = 2A5

.0015u = 1.5n =1n5

4.7k = 4k7

2.5A = 2A5

.0015u = 1.5n =1n5