dBm to mW converter

Type a power level in dBm, such as 20, 0 or −40. The output gives it in milliwatts; the rows give watts, microwatts and dBW too, and the steps show the formula with your number in it.

Swap the boxes to go from power to dBm. Type a power with its unit, such as 1 W, 250 mW or 5 µW; a plain number is read in the unit set under Power in.

dBm is power measured against one milliwatt on a logarithmic scale: P(mW) = 10^(dBm ÷ 10), and dBm = 10 × log10(P in mW). So 0 dBm is exactly 1 mW, 30 dBm is 1 W, and −30 dBm is 1 µW.

The scale turns multiplying into adding. Every +10 dB multiplies the power by 10 and every +3 dB very nearly doubles it, so a 20 dBm transmitter feeding an amplifier with 10 dB of gain puts out 30 dBm. Negative numbers aren't negative power, just less than a milliwatt: received radio signals are usually tiny, which is why phones and Wi-Fi tools show them as negative dBm.

dBW is the same idea measured against 1 watt instead of 1 milliwatt, so dBW = dBm − 30. Plain dB, with no letter after it, is a ratio between two powers, such as a gain or a loss, not a power level by itself.