RF Power dBm Calculator Formula

Understand the math behind the rf power dbm calculator. Each variable explained with a worked example.

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Formulas Used

Power (dBm)

power_dbm = 10 * log10(power_mw)

Power (W)

power_w = power_mw / 1000

RMS Voltage

voltage_rms_mv = sqrt(power_mw / 1000 * impedance_ohm) * 1000

Variables

VariableDescriptionDefault
power_mwPower(mW)100
impedance_ohmSystem Impedance(Ω)50

How It Works

RF Power in dBm

Formulas

dBm = 10 x log10(P_mW)

V_rms = sqrt(P x Z)

dBm is decibels relative to 1 milliwatt. Common values: 0 dBm = 1 mW, 10 dBm = 10 mW, 20 dBm = 100 mW, 30 dBm = 1 W.

Worked Example

100 mW transmitter into 50 ohm system.

power_mw = 100impedance_ohm = 50
  1. 01dBm = 10 x log10(100) = 20 dBm
  2. 02Power = 100 / 1000 = 0.1 W
  3. 03V_rms = sqrt(0.1 x 50) x 1000 = 2236 mV

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