MihsabaHow to use
In a first-order RC circuit, resistance R times capacitance C sets the time constant τ=RC. After one τ, a capacitor charging from zero reaches about 63.2% of the supply, while a discharging capacitor retains about 36.8%. The tool also reports cutoff frequency fc=1/(2πτ) and 5τ settling time.
- Enter R and choose Ω, kΩ or MΩ.
- Enter C with its capacitance unit, then time and voltage.
- Calculate τ, fc, and charging/discharging percentages and voltages at that time.
How it is calculated
Example
Example: R=10 kΩ and C=100 µF give τ=1 s and fc≈0.1592 Hz. At t=1 s with 5 V, charging voltage is ≈3.1606 V and discharging voltage ≈1.8394 V.
Important notes
The equations assume an ideal step source, lumped R and C, and no extra source resistance, ESR, leakage or loading. Real circuits vary with tolerances and conditions; do not rely on this calculator alone for safety-critical design.
Frequently asked questions
Why 63.2% after one τ?
Because 1−e⁻¹≈0.6321 in the exponential charging equation.
Why is 5τ used?
After 5τ, charging reaches about 99.33% and discharge retains about 0.67%, a common practical settling reference.
Does fc apply to every RC circuit?
1/(2πRC) is the ideal one-pole RC −3 dB corner; actual behavior also depends on topology and loading.
Is this calculator free?
Yes. It is free to use and requires no account.