Power is defined as the work done per unit time. The basic unit is watt (W), 1W is equal to 1 joule of work done in 1 second. Commonly used power units are megawatts (1MW=10^6W), kilowatts (1KW=10^3W), milliwatts (1mW=10-3W), microwatts (1μW=10-6W), picowatts (1Pw= 10-12W).

Another commonly used power unit is expressed in decibel milliwatts (dBm). It takes 1 milliwatt as the reference level P0=1mW, and the actual power value P (mW) is compared with P0 and then taken the logarithm. This is the absolute unit of power.

Decibel watts (dBW) can also be used as the power unit, at this time P0=1W, that is, 1 dBW=30 dBm.