Use this for first-order charging, discharging, filter, delay, and transient estimates when resistance and capacitance are known.

The time constant tau equals resistance in ohms multiplied by capacitance in farads. One tau is the characteristic exponential time scale.^[1]

The ideal model assumes lumped, linear components. Source and load resistance, leakage, ESR, tolerances, initial conditions, and threshold choice can materially change a real circuit's timing.

Choose the neighboring tool according to whether you need the inverse conversion, a narrower calculation, or the next step in the workflow.

• Series Resistance Calculator

  Combine resistances before evaluating tau.

• Capacitive Reactance Calculator

  Analyze sinusoidal frequency behavior rather than a transient time scale.

• RC Cutoff Frequency Calculator

  Convert the same R and C values into first-order cutoff frequency.