dBm to Watts

P = 10^((dBm − 30) / 10)

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Result
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Formula

P = 10^((dBm - 30) / 10)

Description

dBm is an absolute power measurement referenced to 1 milliwatt (0.001W), making 0 dBm exactly equal to 1mW. Unlike plain dB which is a ratio, dBm gives you an actual power level. It is the standard unit in RF engineering, telecommunications, and fiber optics because it allows signal power levels spanning many orders of magnitude to be expressed as manageable numbers. The conversion subtracts 30 because 1mW = 10^(-3)W, and -3 in the exponent becomes -30 when scaled by the factor of 10 in the dB formula.

Variables

  • dBm — Absolute power level referenced to 1mW
  • P — Power in watts (W)

Practical Notes

Common reference points: 0 dBm = 1mW, 10 dBm = 10mW, 20 dBm = 100mW, 30 dBm = 1W, -30 dBm = 1µW. WiFi transmitters typically operate at 15-20 dBm (30-100mW). Cell towers transmit at 43-46 dBm (20-40W). The dBm scale is implicitly referenced to 50Ω impedance in RF systems and 600Ω in audio.

Related Formulas

dB (Power) dB (Voltage) dBV (Voltage Level) dBu (Voltage Level) dBm to dBW Conversion Receiver Noise Floor

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