System International (SI) Notation

SI Notation

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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.

Using SI notation the unit of measurement appears at the end of the value. Multipliers may also be used, (taking the place of the decimal point in the old system). 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:-

2.2k = 2k2

4.7k = 4k7

2.5A = 2A5

.0015u = 1.5n =1n5

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

Number	Prefix	Symbol
10 ³	kilo	k
10 ⁶	mega	M
10 ⁹	giga	G
10 ¹²	tera	T

Number	Prefix	Symbol
10 ^-3	milli	m
10 ^-6	micro	u
10 ^-9	nano	n
10 ^-12	pico	p

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