RC Filter Calculator

Written by Great Medico

Updated September 25, 2026 •2 min read

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Electrical shortcut formulas are useful only when phase, units, and circuit assumptions are kept straight. RC Filter Calculator targets RC cutoff frequency and shows the relationship behind the number rather than treating it as a black-box design approval.

What this calculator does

The RC Filter Calculator centers on RC cutoff frequency using the fields that are actually present here: Resistance (R), Capacitance (C), Cutoff frequency (fc), Select filter type. Rather than treating every box as an independent input, use the equation below to identify the driving quantities and read the remaining fields as derived or supporting values when appropriate.

How to use it

Enter any two among resistance, capacitance, and cutoff frequency. Select low-pass or high-pass for context; the corner-frequency magnitude uses the same RC equation.

How the calculation works

For a first-order RC filter, fc = 1/(2πRC). The page rearranges the same relation to solve R or C when cutoff frequency and the other component are supplied. Low-pass and high-pass selections share the same −3 dB corner-frequency equation.

Example

With R = 1 kΩ and C = 1 µF, fc = 1/(2π×1000×10⁻⁶) ≈ 159.15 Hz.

How to interpret the result

For RC Filter Calculator, read RC cutoff frequency in the context of the equation above. Interpret the result as the output of the stated circuit relationship, not as automatic confirmation that a component, conductor, or installation is adequately rated. Cross-check units and phase convention, then apply real equipment limits and applicable electrical standards separately.

Limitations and notes

This is the ideal single-pole corner frequency. Source resistance and load impedance can change the effective R, while capacitor tolerance, ESR, leakage, and parasitics alter real response. The filter-type selector changes the interpretation of which frequencies pass; it does not change the basic fc formula.