decibelmilliwatts

Decibel-milliwatts, abbreviated dBm, is a logarithmic unit used to express power levels in radio engineering. It represents a power level as a decibel quantity relative to 1 milliwatt. The defining relation is P(dBm) = 10 log10(P / 1 mW), where P is the power in watts. Equivalently, if P is measured in milliwatts, P(dBm) = 10 log10(PmW).

Because the decibel is a ratio, dBm is a logarithmic expression of power with a fixed reference, making it effectively an absolute power level. It is widely used for transmitter output, received power, and link budgets, especially in wireless communications and RF measurement, including devices like spectrum analyzers and power meters. It is commonly contrasted with dBW, which uses 1 watt as the reference.

Conversions and examples illustrate its use. 0 dBm equals 1 mW; 10 dBm equals 10 mW; 20 dBm equals 100 mW; 30 dBm equals 1 W. In general, P(W) = 1e-3 × 10^(dBm/10). Negative dBm values indicate powers below 1 mW; for example, -30 dBm is 1 µW. Typical practical ranges span from about -100 dBm (very weak received signals) to around +30 dBm (a few tens of milliwatts to a watt) for certain transmitters, with many wireless links operating in the -40 to -80 dBm range at the receiver.