dBm ↔ Power ↔ Attenuation Calculator

RF measurement calculator for spectrum analyzer work with external attenuators

Computes the actual source power from a power level measured on a spectrum analyzer, given the sum of external step-attenuator values and the analyzer's internal attenuation setting. Also converts directly between dBm and watts, and between dBm and RMS/peak-to-peak voltage across a chosen system impedance (default 50 Ω), which is useful when comparing analyzer readings to oscilloscope or signal generator values.

Step 1: Calculation Mode

Measured → Source

dBm ↔ W Converter

dBm ↔ Voltage (50 Ω)

Step 2: Input Parameters

Measured Power (P_meas) [dBm]:

External Attenuator (toggle buttons):

Total External Attenuation: 0 dB

Internal Attenuation (L_int) [dB]:

System Impedance (R) [Ω]:

Step 3: Results

Basic Formulas

Attenuation and dBm

P_out[dBm] = P_in[dBm] − L[dB]
P_in[dBm] = P_out[dBm] + L[dB]
With analyzer measurement: P_src[dBm] = P_meas[dBm] + L_ext[dB] + L_int[dB]

dBm ↔ W

P[mW] = 10^(P[dBm] / 10)
P[W] = 10^((P[dBm] − 30) / 10)
P[dBm] = 10 · log₁₀(P[mW])

Power ↔ Voltage for resistive load R

P[W] = (V_rms²) / R
V_rms = √(P[W] · R)
V_pp = 2 · √2 · V_rms ≈ 2.828 · V_rms