This page defines the term "dBm" and provides some helpful advice.

dBm is an absolute measure of power.

• the m stands for milli watts
• to convert dBm to watts we divide by ten and then take the inverse log in base 10
• so 0dBm = 1 mW

– 0/10 = 0

– 10⁰ = 1

• 10 dBm = 10 mW
• 20 dBm = 100 mW
• 30 dBm = 1,000 mW = 1 W
• using dBm is helpful when looking at power through circuits, as we can simply add the gain and subtract the attenuation in dB and end up with a final power number in dBm
• you can also use dBW

– where 0dBW = 1 Watt