RC Circuit Calculator

Free RC Circuit Calculator — compute time constant, cutoff frequency, charging and discharging voltages for any RC network.

982.0K uses Updated · 2026-05-11 Runs locally · zero upload
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The RC Circuit Calculator solves the most common RC questions: time constant τ, cutoff frequency fc and the instantaneous capacitor voltage during charging or discharging.

How to Use RC Circuit Calculator

  1. Pick a mode — Charging, Discharging or Cutoff Frequency.
  2. Enter R and C — values with units (Ω, kΩ, MΩ; pF, nF, μF, mF, F).
  3. Fill in mode-specific fields — Vs/V0/t for charging, V0/t for discharging.
  4. Read τ, fc and Vc(t) — the RC Circuit Calculator also shows when the response settles (5τ).

Formula & Theory — RC Circuit Calculator

τ = R · C
fc = 1 / (2π R C)
Vc(t) = Vs + (V0 − Vs) · e^(−t/τ)
Vc(t) = V0 · e^(−t/τ)   (discharging to 0)

Use Cases for RC Circuit Calculator

  • Filter design — choose R and C for a desired low-pass or high-pass cutoff.
  • Microcontroller circuits — size debounce, reset and timing networks.
  • Power electronics — estimate inrush, soft-start and decoupling behaviour.
  • Education — verify textbook RC charging/discharging problems step by step.

Frequently asked questions about RC Circuit Calculator

What is the RC time constant?

τ = R·C is the time required for the capacitor voltage to change by 63.2% toward its final value during charging, or to fall to 36.8% during discharging.

When is an RC circuit considered stable?

After about 5 time constants (5τ) the capacitor voltage is within ~1% of its final value, which is generally treated as steady state.

What is the cutoff frequency?

fc = 1 / (2π R C) marks the −3 dB point of the RC filter response.

Is my data stored?

No. All calculations run locally in your browser; nothing is sent to any server.