RC Time Constant Calculator
A first-order RC time constant describes the response speed of a circuit made from a resistance and capacitance. The calculator also estimates the five-time-constant interval and cutoff frequency.
How to use this calculator
- Enter resistance in ohms and capacitance in microfarads. The calculator converts microfarads to farads before applying the equations.
- Check the labels and units before applying the result to a real task.
- Change one input at a time when comparing scenarios.
Formula and method
τ = RC; f_c = 1/(2πRC)
- τ = RC; f_c = 1/(2πRC)
- These equations describe a simple first-order RC network. Actual response depends on topology, source/load impedance and component parasitics.
Worked examples
Worked example
A 10,000 Ω resistor and 10 µF capacitor.
τ = 10,000×10×10⁻⁶ = 0.1 seconds; cutoff frequency is about 1.59 Hz.
τ = 10,000×10×10⁻⁶ = 0.1 seconds; cutoff frequency is about 1.59 Hz.
Understanding the result
A first-order RC time constant describes the response speed of a circuit made from a resistance and capacitance. The calculator also estimates the five-time-constant interval and cutoff frequency.
These equations describe a simple first-order RC network. Actual response depends on topology, source/load impedance and component parasitics.
Important notes
These equations describe a simple first-order RC network. Actual response depends on topology, source/load impedance and component parasitics.
Displayed values are rounded for readability; retain appropriate precision when continuing a calculation.
Frequently asked questions
What does one time constant mean?
For a simple charging or discharging response, one time constant corresponds to about 63.2% of the total change completed or about 36.8% of the initial difference remaining.
Why is five time constants shown?
Five time constants is a common approximation for near-settled first-order behaviour, but it is not an exact endpoint.
Does the cutoff frequency apply to every RC circuit?
The expression applies to the relevant first-order RC low-pass or high-pass configuration. Other circuit arrangements need their own transfer function.
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Related explanations
Learn the method behind the number or compare the terminology before using the calculator.
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This page provides a calculation tool plus explanatory information so you can understand what the result means and when the underlying method may not fit your situation.