3 dB Attenuator Calculator

Use this tool to calculate Resistor values for a 3 dB Pi Attenuator circuit.

3 dB is the default attenuation value below and the characteristic impedance is 50 ohm. Both values can be changed.


R1 = Zo [10dB/20 + 1] / [10dB/20 – 1]

R2 = Zo/2 [10dB/10 – 1] / [10dB/20]

where R1 is the shunt resistor and R2 is the series resistor. To build this 3 dB attenuator you will need

  • two 292.40 ohm shunt resistors – one at the input and the other at the output
  • one 17.61 ohm series resistor