SI units:
Units for electrical quantities are defined by the International System of Units, or SI. Common units are:
| Quantity | Unit | Symbol |
|---|---|---|
| Current | ampere | A |
| Capacitance | farad | F |
| Inductance | henry | H |
| Resistance | ohm | Ω (or, non standard, R) |
| Voltage | volt | V |
| Power | watt | W |
Strict usage is that units are not capitalized but the symbols are capital letters.
There are various prefixes used to denote power of 10 multiples or divisions of these units. For example, a milliwatt is 1/1000 of a watt. The prefixes commonly used in electronics are:
| Name | Multiplier | Symbol |
|---|---|---|
| mega | 1,000,000 | M |
| kilo | 1000 | k |
| milli | 1/1000 | m |
| micro | 1/1,000,000 | µ (or, non standard, u) |
| nano | 1/1,000,000,000 | n |
| pico | 1/1,000,000,000,000 | p |
Note the capitalization of the symbols: M and m mean very different things.
A farad is an extremely large capacitance so you usually see µF, nF, or pF. On the other hand an ohm is a small resistance so you often see kΩ or MΩ.