RC and RL Filter Cutoff Calculator
Calculate the −3 dB cutoff frequency and time constant τ of first order RC and RL filters, plus the 5τ settling time.
Runs on your device
Result
Results appear here as you type.
What it does
For an RC filter, fc = 1 / (2πRC) and τ = RC. For an RL filter, fc = R / (2πL) and τ = L / R. After 5τ a step response has settled to within 1% of its final value.
How to use it
- Choose RC or RL.
- Enter R and C (or L).
- Read fc, τ and settling time.
Example
10 kΩ and 100 nF: fc ≈ 159.2 Hz, τ = 1 ms. Select Try an example above to see it.
When it helps
- Designing antialiasing filters.
- Debouncing switches.
- Signals and systems coursework.
Questions
Is it low pass or high pass?
Both have the same cutoff. It depends on which component the output is taken across.
What does −3 dB mean?
At fc the output power is half the input (amplitude about 70.7%).
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