This calculator computes the time constant τ = R × C of a resistor–capacitor (RC) circuit. You can also see how much a capacitor has charged at a given time t for a simple RC charging circuit.
An RC time constant describes how quickly a resistor–capacitor circuit charges or discharges. It is defined as τ = R × C, where R is resistance in ohms (Ω) and C is capacitance in farads (F). The unit of τ is seconds.
For a simple RC charging circuit, the voltage across the capacitor as a function of time is:
V(t) = Vfinal · (1 − e−t/τ)
After one time constant (t = τ), the capacitor reaches about 63.2% of its final voltage. After 5 time constants it is above 99% and often treated as "fully charged" for practical purposes.
This calculator is suitable for basic electronics design, timing circuits, filters, Arduino projects and educational use. It assumes ideal components and simple first-order RC behaviour.
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