Use this tool to calculate resistor values for a Pi attenuator pad.
These attenuators are used in Radio Frequency (RF) circuits.
Enter the desired value of attenuation and the characteristic impedance The default value is 50 ohm. However it can be changed to any arbitrary value – for instance 75 ohm.
Calculator
Formula
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 attenuator you will need
- two shunt resistors – one at the input and the other at the output
- one series resistor
Pi Attenuator Table
Below is a table of resistor values for attenuation values from 1dB to 50 dB. The impedance value is 50 ohm.
| Attenuation (dB) | R1 (Ohm) | R2 (Ohm) |
| 1 | 869.5 | 5.8 |
| 2 | 436.2 | 11.6 |
| 3 | 292.4 | 17.6 |
| 4 | 221.0 | 23.8 |
| 5 | 178.5 | 30.4 |
| 6 | 150.5 | 37.4 |
| 7 | 130.7 | 44.8 |
| 8 | 116.1 | 52.8 |
| 9 | 105.0 | 61.6 |
| 10 | 96.2 | 71.2 |
| 11 | 89.2 | 81.7 |
| 12 | 83.5 | 93.2 |
| 13 | 78.8 | 106.1 |
| 14 | 74.9 | 120.3 |
| 15 | 71.6 | 136.1 |
| 16 | 68.8 | 153.8 |
| 17 | 66.4 | 173.5 |
| 18 | 64.4 | 195.4 |
| 19 | 62.6 | 220.0 |
| 20 | 61.1 | 247.5 |
| 21 | 59.8 | 278.3 |
| 22 | 58.6 | 312.7 |
| 23 | 57.6 | 351.4 |
| 24 | 56.7 | 394.6 |
| 25 | 56.0 | 443.2 |
| 26 | 55.3 | 497.6 |
| 27 | 54.7 | 558.6 |
| 28 | 54.1 | 627.0 |
| 29 | 53.7 | 703.7 |
| 30 | 53.3 | 789.8 |
| 31 | 52.9 | 886.3 |
| 32 | 52.6 | 994.6 |
| 33 | 52.3 | 1116.1 |
| 34 | 52.0 | 1252.5 |
| 35 | 51.8 | 1405.4 |
| 36 | 51.6 | 1577.0 |
| 37 | 51.4 | 1769.5 |
| 38 | 51.3 | 1985.5 |
| 39 | 51.1 | 2227.8 |
| 40 | 51.0 | 2499.8 |
| 41 | 50.9 | 2804.8 |
| 42 | 50.8 | 3147.1 |
| 43 | 50.7 | 3531.2 |
| 44 | 50.6 | 3962.1 |
| 45 | 50.6 | 4445.6 |
| 46 | 50.5 | 4988.0 |
| 47 | 50.4 | 5596.7 |
| 48 | 50.4 | 6279.6 |
| 49 | 50.4 | 7045.9 |
| 50 | 50.3 | 7905.6 |