Free Online Tool

Filter Calculator

Calculate the cutoff frequency of RC or RL low-pass and high-pass filters from resistor, capacitor, and inductor values.

The result will appear here.

How to Use

  1. Choose RC filter or RL filter circuit.
  2. Choose low-pass or high-pass filter type.
  3. Enter resistance and capacitance or inductance with units.
  4. Review the cutoff frequency and the formula used.

Examples

  • Calculate an RC cutoff frequency from 100Ω and 10µF
  • Calculate an RL cutoff frequency from 10Ω and 10mH

Calculation and Conversion Notes

The cutoff frequency of an RC filter is calculated as fc = 1 / (2πRC). The cutoff frequency of an RL filter is calculated as fc = R / (2πL). Low-pass and high-pass filters use the cutoff frequency as the same reference point, but they pass or attenuate different frequency ranges. At the cutoff frequency, the output is about 70.7% of the input, or -3 dB.

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