Filter Cutoff Frequency Calculator
Calculate the corner frequency of RC and LC filters and the roll-off they achieve.
About Filter Cutoff Frequency Calculator
Each filter order adds 20 dB per decade of roll-off, so a second-order filter falls at 40 dB per decade. Cutoff is conventionally the half-power point, 3 dB below the passband. Steeper filters need higher order, which costs components and introduces phase distortion and potential ringing near cutoff.
Formula
Filter Cutoff Frequency
RC: f_c = 1 ÷ (2πRC); LC: f_c = 1 ÷ (2π√(LC)); roll-off = 20n dB/decade
- order
- Number of reactive elements, setting the roll-off steepness
- 3 dB point
- Cutoff is defined where power halves
Worked example
With the default values below, Filter Cutoff Frequency Calculator returns RC Cutoff Frequency of 1,591.549. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Resistanceminimum 0.01 ohm
- 1,000 ohm
- Capacitanceminimum 0 F
- 0 F
- Inductance for an LC filterminimum 0 H
- 0.001 H
- Filter orderaccepts 1–8
- 1
Results
- RC Cutoff Frequency
- 1,591.549 Hz
- LC Cutoff Frequency
- 15,915.494 Hz
- Roll-Off Rate
- 20 dB/decade
- Roll-Off Rate
- 6 dB/octave
- Attenuation One Decade Beyond Cutoff
- 20.0 dB
Step by step
- 1Values used
- 2Filter Cutoff Frequency
- 3RC Cutoff Frequency= 1,591.549 Hz
- 4LC Cutoff Frequency= 15,915.494 Hz
- 5Roll-Off Rate= 20 dB/decade
- 6Roll-Off Rate= 6 dB/octave
- 7Attenuation One Decade Beyond Cutoff= 20.0 dB
Assumptions and limits
- The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
How is Filter Cutoff Frequency calculated?
RC: f_c = 1 ÷ (2πRC); LC: f_c = 1 ÷ (2π√(LC)); roll-off = 20n dB/decade Each filter order adds 20 dB per decade of roll-off, so a second-order filter falls at 40 dB per decade. Cutoff is conventionally the half-power point, 3 dB below the passband.
Why does Filter Cutoff Frequency matter?
Steeper filters need higher order, which costs components and introduces phase distortion and potential ringing near cutoff.
What values do I need to enter?
This calculator takes 4 inputs: Resistance, Capacitance, Inductance for an LC filter, Filter order. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.