Resistive Attenuator Calculator

Design simple resistive attenuator pads between equal impedances (e.g., 50 Ω systems). This tool computes resistor values for classic T (tee) and π (pi) pads given a target attenuation in dB and a characteristic impedance Z₀.

Current version assumes equal source and load impedances (Z_S = Z_L = Z₀). For impedance-transforming designs, see the Network Matching Tool.

Quick Overview

T-pad: two series arms with a shunt resistor between them.
π-pad: two shunt resistors with a single series resistor between ports.

All formulas assume resistive networks at the design impedance. Real components have tolerance, power limits, and frequency dependence. For high power, derate generously.

Input Parameters

Attenuator topology

Choose the resistor network style. Both assume Z_S = Z_L = Z₀.

Characteristic impedance Z₀ (Ω)

Typically 50 Ω for RF work (75 Ω, 600 Ω, etc. also supported).

Attenuation (dB)

Positive insertion loss (e.g., 3, 6, 10, 20 dB).

Power handling

Input power P_in (W)

Maximum RF power you expect to apply to the pad. Set to > 0 to compute resistor dissipation.

Safety margin (%)

Multiplier on calculated resistor dissipation. For example, 50 % → design for 1.5× the computed power.

Formulas use standard equal-impedance pad equations with K = 10^A_dB/20 as the voltage ratio (V_in/V_out).

Results

Attenuation (A_dB)

6.00 dB

Voltage ratio K = V_in / V_out

1.995

Power ratio P_in / P_out

3.981

T (tee) pad – equal impedances

Two series resistors R₁ and R₃ with a shunt resistor R₂ between them, matched to Z₀ on both ports.

R₁ = R₃ (series)

16.614 Ω

R₂ (shunt to ground)

66.931 Ω

Input power P_in

10.00 W

Output power P_out (approx.)

2.68 W

Total pad dissipation

7.32 W

Resistor wattage (with safety margin)

Resistor	Value (Ω)	Dissipation (W)	With margin (W)	Suggested rating
R₁	16.614	0.890	1.335	2 W
R₂	66.931	5.543	8.314	10 W
R₃	16.614	0.890	1.335	2 W

Power is approximate for sinusoidal RF at the specified P_in with matched terminations. For very high power or pulsed operation, add additional margin.

For higher power builds, consider using parallel resistors to reduce dissipation per element and improve thermal handling.