Attenuator Pad (π and T) Resistor Calculator
Resistor values for T and π attenuator pads from the required attenuation in dB and the system impedance.
Worked example
Input: Attenuation 10 dB, System impedance Z₀ 50 Ω
Result: T pad: series resistor R₁ (each side) 25.9747 Ω, T pad: shunt resistor R₂ 35.1364 Ω, π pad: shunt resistor R_sh (each side) 96.2475 Ω, π pad: series resistor R_se 71.1512 Ω
Result: T pad: series resistor R₁ (each side) 25.9747 Ω, T pad: shunt resistor R₂ 35.1364 Ω, π pad: shunt resistor R_sh (each side) 96.2475 Ω, π pad: series resistor R_se 71.1512 Ω
Formula
K = 10^(A/20)
T-pad: R₁ = Z₀(K−1)/(K+1), R₂ = 2K·Z₀/(K²−1)
π-pad: R_sh = Z₀(K+1)/(K−1), R_se = Z₀(K²−1)/(2K)
How it works
An attenuator is a resistive network that reduces the signal while keeping the input and output impedance at Z₀. With K = 10^(A/20), the T-pad series resistor is Z₀(K−1)/(K+1) and the shunt resistor is 2K·Z₀/(K²−1). At 50 Ω, 10 dB gives about 26 Ω / 35 Ω for a T pad and 96 Ω / 71 Ω for a π pad.
Practical tipRounding to the nearest standard resistor values slightly degrades the impedance match. For higher power check the resistor power rating and frequency behavior. For pads that protect a receiver or amplifier input, measure the insertion loss with a network analyzer before testing.
Related calculators
Results and summaries are for reference. For certification and test reports use the latest official standard text and calibrated instrument data. Last updated: 2026-10-10