dBm to Watts Calculator
Convert dBm to watts, milliwatts and dBW, or go the other way, for RF and optical power.
Reference levels
| dBm | Milliwatts | Watts |
|---|---|---|
| -100 dBm | 1.0e-10 mW | 1.0e-13 W |
| -80 dBm | 1.0e-8 mW | 1.0e-11 W |
| -60 dBm | 1.0e-6 mW | 1.0e-9 W |
| -40 dBm | 0.0001 mW | 1.0e-7 W |
| -30 dBm | 0.001 mW | 1.0e-6 W |
| -20 dBm | 0.01 mW | 1.0e-5 W |
| -10 dBm | 0.1 mW | 0.0001 W |
| 0 dBm | 1 mW | 0.001 W |
| 10 dBm | 10 mW | 0.01 W |
| 20 dBm | 100 mW | 0.1 W |
| 30 dBm | 1,000 mW | 1 W |
| 40 dBm | 10,000 mW | 10 W |
| 50 dBm | 100,000 mW | 100 W |
What dBm means
dBm is power expressed on a decibel scale referenced to one milliwatt. So 0 dBm is 1 mW, by definition:
P(W) = 10^((dBm − 30) / 10)
dBm = 10 × log₁₀(P(W)) + 30
dBW uses one watt as the reference instead, so it is simply
dBm − 30.
The numbers worth remembering
- +3 dB doubles the power; −3 dB halves it.
- +10 dB is ten times the power; +20 dB is a hundred times.
- 0 dBm = 1 mW, 30 dBm = 1 W, 60 dBm = 1 kW.
Those two rules let you do most RF arithmetic in your head: 23 dBm is 20 dBm (100 mW) plus 3 dB, so 200 mW.
Why a log scale at all
Radio power spans an enormous range — a phone transmits at about 23 dBm (0.2 W) and receives usable signal down around −110 dBm, which is 0.00000000001 mW. Decibels compress that into readable numbers, and turn the multiplications of gains and losses along a signal chain into simple addition.
Wi-Fi signal strength is quoted in dBm and is always negative: −50 dBm is excellent, −70 dBm is workable, −85 dBm is close to unusable.