Enter any two values to find the third one:

About this calculator

Note that you can enter values in typical formats. Case is ignored.

  • For frequencies, '10k', '5KHZ','8MHz' and '1M' are all valid.
  • For resistors, '100R', '470r', '1k2','47k', '2M2', and '10M' are all valid.
  • For capacitors, '22p', '330p', '2n2', '10nF', '4.7u', '4u7', and '22uF' are all valid.

Since case is ignored, 'milli' prefixes will be interpreted as 'Mega'. This only really affects frequency.

A '1% resistor' usually means +/-1% tolerance. This calculator works this way. 10% is +/-10%.

Capacitors and Resistors are both limited to a 'typical' range; 10pF to <10000uF for caps, 1Ω to <100MΩ for resistors. Outside this range things will probably turn to nonsense.

4 Responses to “RC Filter Calculator”

  1. Ernest Dines

    The time constants don’t seem to be right. For 1M, 1nF, I’m getting 6.3ms. Should it not be 1ms?

    • Tom Wiltshire

      Well spotted, Ernest. Thanks very much for that. It used to be ok, so it looks like it lost a “2 Pi” term in the transfer to the new website.
      Now corrected.


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