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dBm to Watts Calculator
Convert power levels between dBm, watts, and milliwatts.
Conversion Direction
Formulas
Result (mW)
mW
—
Watts
—
Reference Table
| dBm | mW | W |
|---|---|---|
| -10 dBm | 0.1 mW | 0.0001 W |
| 0 dBm | 1 mW | 0.0010 W |
| 10 dBm | 10 mW | 0.0 W |
| 20 dBm | 100 mW | 0.1 W |
| 30 dBm | 1,000 mW | 1.0 W |
| 40 dBm | 10,000 mW | 10.0 W |
Understanding dBm Power Units
dBm (decibels relative to one milliwatt) is a logarithmic unit used in RF, telecommunications, and audio engineering. It allows a huge dynamic range — from nanoWatts to kiloWatts — to be expressed in a manageable number scale.
The Conversion Formulas
Watts to dBm: P(dBm) = 10 × log₁₀(P_mW) = 10 × log₁₀(P_W × 1000)
dBm to Watts: P(mW) = 10^(dBm/10); P(W) = P(mW) / 1000
Common Reference Points
| dBm | Power | |-----|-------| | −120 dBm | 1 femtowatt (noise floor) | | −70 dBm | 100 picowatts (weak cellular signal) | | 0 dBm | 1 milliwatt (standard RF reference) | | +10 dBm | 10 milliwatts (WiFi transmit power) | | +20 dBm | 100 milliwatts | | +30 dBm | 1 watt | | +43 dBm | 20 watts (typical mobile base station) |
How to Use This Calculator
Enter power in dBm to get watts and milliwatts, or enter watts/milliwatts to get dBm. The calculator also shows the conversion for adding/subtracting dB values.
Practical Examples
Example 1: WiFi router transmits at 20 dBm. Power = 10^(20/10) = 100 mW = 0.1W.
Example 2: Received signal −85 dBm. Power = 10^(−85/10) = 3.16 × 10⁻⁹ W = 3.16 nW — the receiver must detect this faint signal reliably.