RC Time Constant Calculator
Calculate the time constant of an RC circuit.
Formula
τ = RC.
What Is an RC Time Constant?
The RC time constant describes how quickly a capacitor charges or discharges through a resistor. One time constant equals resistance multiplied by capacitance and is measured in seconds.
Example Calculation
For R = 10,000 Ω and C = 100 µF (0.0001 F), τ = 10,000 × 0.0001 = 1 second.
Factors and Interpretation
Increasing either resistance or capacitance increases the time constant. After one τ, a charging capacitor reaches about 63.2% of its final voltage; after about five τ it is effectively fully charged for many practical purposes.
Frequently Asked Questions
Is τ the full charging time?
No. It is a characteristic time; practical full charge is commonly approximated near five time constants.
What units should I enter?
Use ohms and farads to obtain seconds.
Does the same τ apply to discharge?
Yes, for the same resistance and capacitance the discharge follows the same time constant.
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Formula and Practical Limits
The RC time constant is τ = RC. After one time constant a charging capacitor reaches about 63.2% of its final voltage in the ideal first-order model; practical circuits can include source resistance, leakage and component tolerance.