RF Power dBm Calculator Formula
Understand the math behind the rf power dbm calculator. Each variable explained with a worked example.
Formulas Used
Power (dBm)
power_dbm = 10 * log10(power_mw)Power (W)
power_w = power_mw / 1000RMS Voltage
voltage_rms_mv = sqrt(power_mw / 1000 * impedance_ohm) * 1000Variables
| Variable | Description | Default |
|---|---|---|
power_mw | Power(mW) | 100 |
impedance_ohm | System 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
- 01dBm = 10 x log10(100) = 20 dBm
- 02Power = 100 / 1000 = 0.1 W
- 03V_rms = sqrt(0.1 x 50) x 1000 = 2236 mV
Frequently Asked Questions
Why use dBm?
dBm simplifies gain/loss calculations to addition/subtraction. A +20 dBm signal through a 3 dB loss becomes +17 dBm.
dBm vs dBW?
dBm is referenced to 1 mW, dBW to 1 W. dBW = dBm - 30. Both are absolute power units.
What does negative dBm mean?
Power less than 1 mW. Wi-Fi receiver sensitivity is typically -70 to -90 dBm (picowatts).
Ready to run the numbers?
Open RF Power dBm Calculator