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First-Order RC & RL Corner Frequency

Find the ideal first-order corner frequency for a selected RC or RL circuit model.

Formula & worked example
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How to use this calculator

Enter the known values in the units shown. Results update as you type.
Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
Use the worked example to check the method. Reset restores the starting fields.

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Formula and method

An RC time constant of 1 second gives corner frequency 1/(2π) Hz, about 0.159155 Hz. For RL, the corresponding time constant is L/R.

RC: fc = 1/(2πRC); RL: fc = R/(2πL)

Worked example

Enter these known values and leave the other values blank.

Effective circuit resistance: 1000 Ω
Capacitance: 1000 μF

RC corner frequency: 0.15915 Hz

Assumptions and limitations

This is an ideal component model. Losses, tolerances, temperature dependence, parasitics and component ratings require separate information.
These formulas describe a first-order RC or RL response. Output placement determines whether the response is high-pass or low-pass.
Use the effective resistance seen by the reactive component in the intended topology. Additional source or load resistance can change the corner frequency.
Resistance, capacitance, inductance and frequencies must be positive. The two modes share the resistance field, but have separate reactive components and frequency fields.

Common questions

Is the same formula valid for any filter order?

No. Higher-order networks and loaded circuits require their own transfer-function model.

What is special about the corner frequency?

For the ideal first-order response, its magnitude is 1/√2 of the passband gain at that frequency, approximately −3.01 dB.

References

The calculation equations, inverse formulas, units, and input rules were imported from this source. Bookify provides the interface and equation solver.

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