How the calculation works
RF power is commonly expressed in linear units such as watts and milliwatts, or in logarithmic units such as dBW and dBm.
dBW = 10 × log10(P in W)
dBm = 10 × log10(P in mW)
Because 1 watt equals 1000 milliwatts, the two decibel scales are always separated by 30 dB:
dBm = dBW + 30
When a resistive load is known, the equivalent voltage can also be estimated from:
P = V² / R → Vrms = √(P × R)
Worked example
Enter a value above to see the calculation worked through here.
Practical RF landmarks
Some power values appear repeatedly in radio work. 0 dBm is 1 mW. 10 dBm is 10 mW. 20 dBm is 100 mW. 30 dBm is 1 W. 40 dBm is 10 W. 50 dBm is 100 W.
About the voltage results
The voltage section assumes a purely resistive load such as an ideal 50 Ω or 75 Ω system. In real RF systems, reactive components and mismatch can change the actual measured voltage.