RF Power Conversion Calculator. The RF Power Conversion Calculator converts radio frequency power values between the four units used in wireless and electronics work: milliwatts (mW), watts (W), dBm, and dBW. Enter your Power Value, select your Input Unit and Output Unit to get the Converted Power — plus a full breakdown showing your value expressed in all four units simultaneously. Also try the kW to kWh Calculator.
dBm is decibels referenced to 1 milliwatt (0 dBm = 1 mW), while dBW is decibels referenced to 1 watt (0 dBW = 1 W). dBW is 30 dB higher than dBm for the same power level. See also our Amps to kW Calculator.
To convert watts to dBm: dBm = 10 × log₁₀(Power in watts × 1000). For example, 1 watt = 30 dBm, and 0.001 watts (1 mW) = 0 dBm.
Decibel units are used because they make calculations easier when dealing with gains and losses in RF systems. You can simply add and subtract dB values instead of multiplying and dividing power ratios.
0 dBm equals exactly 1 milliwatt or 0.001 watts. This is the reference point for dBm measurements in RF power calculations.
Yes, negative dBm values represent power levels below 1 milliwatt. For example, -10 dBm equals 0.1 mW, and -30 dBm equals 0.001 mW (1 microwatt).
dBW = dBm - 30. This is because 1 watt = 1000 milliwatts, and 10 × log₁₀(1000) = 30 dB. So any power level in dBW is 30 dB less than the same power in dBm.
Cell phones typically transmit at +20 to +30 dBm (100 mW to 1 W), Wi-Fi routers at +20 dBm (100 mW), and Bluetooth devices at 0 to +4 dBm (1 to 2.5 mW).
RF power conversions using standard formulas are mathematically exact. However, real-world measurements may vary due to equipment tolerances, temperature effects, and impedance mismatches in the RF system. You might also find our find Voltage with Joules to Volts Calculator useful.