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Resistive Pi Attenuator Design

Calculate ideal equal- or unequal-impedance pi-pad resistors.

  • Formula & worked example
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Calculator inputs

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How to use this calculator

  1. Enter the known values in the units shown. Results update as you type.
  2. Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
  3. Use the worked example to check the method. Reset restores the starting fields.

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Formula and method

The worked inputs demonstrate the selected model; change a known value or leave an editable unknown empty for a supported inverse.

K=10^(A/20); equal shunt=Z(K+1)/(K−1), series=Z(K−1/K)/2

Worked example

Enter these known values and leave the other values blank.

Attenuation (in decibels)
20 dB​
Impedance (Z==0==)
50 Ω
Resistor 1 (R==1==)
61.11 Ω
Resistor 2 (R==2==)
247.5 Ω

Assumptions and limitations

  • Source and load impedances are positive real resistances. The circuit is ideal, frequency independent and uses no parasitics or component power limits.
  • Finite positive resistor designs require positive attenuation; unequal impedances impose an additional minimum loss.

Common questions

What does this model assume?

Source and load impedances are positive real resistances. The circuit is ideal, frequency independent and uses no parasitics or component power limits. Finite positive resistor designs require positive attenuation; unequal impedances impose an additional minimum loss.

How do units and inverse calculations work?

Choose compatible units for each quantity. The model converts quantities internally; supported editable fields can be solved from sufficient independent known values. Display rounding does not change the underlying value.

References

Explicit model domains enforce physical bounds and strict whole-count membership where required. Explanatory image content is replaced by original dimension descriptions without changing its visibility. Unequal-impedance attenuation exceeds the positive-resistor feasibility threshold; residual-sign tests avoid tolerance-based equality at that boundary.

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