dBm to mW Converter (and Watts, dBW)

How it works

dBm expresses power relative to 1 milliwatt on a logarithmic scale: 0 dBm is 1 mW, every +10 dB is ten times more power and every +3 dB roughly doubles it.

Logarithmic units make link budgets easy: add transmit power and antenna gains in dB, subtract cable and path losses, and compare the result with the receiver's sensitivity.

P(mW) = 10^(dBm / 10)
dBm = 10 × log10(P in mW)
dBW = dBm − 30

Worked example

A radio transmitting at 20 dBm outputs 10^(20/10) = 100 mW. 14 dBm, a common LoRa limit in Europe, is about 25.1 mW, and a received signal of −120 dBm is just 1 × 10⁻¹⁵ W (one femtowatt).