Circuit Analysis calculator
RC Circuit Calculator
This RC circuit calculator focuses on first-order resistor–capacitor networks. Given resistance R, capacitance C, and (optionally) applied voltage or frequency, it evaluates the time constant τ = R×C, step-response voltages for charging and discharging, cutoff frequency fc = 1/(2πRC), capacitive reactance Xc = 1/(2πfC), basic filter gain, and phase shift. For a timing check, 10 kΩ x 10 µF gives τ = 100 ms; for a simple filter check, 1 kΩ x 0.1 µF gives fc = 1.59 kHz. The intent is to support practical timing networks, low-pass and high-pass filters, integrators, differentiators, and simple snubber calculations for low- and medium-voltage analog or control circuits. Final component selection must still follow device datasheets, manufacturer guidance, and applicable codes.
Updated July 16, 2026
τ = R × C | 10kΩ × 10μF = 100ms time constant | fc = 1/(2πRC)
Charging: 1τ = 63.2% | 3τ = 95% | 5τ = 99% of final voltage
Enter R and C values for instant time constant and cutoff frequency
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Field kit
Bench kit for RC circuits
Use the time constant or cutoff result to build a low-voltage bench example and verify parts before using the circuit.
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Calculation history
Example Calculations
How to Use
How to use this RC circuit calculator
This tool shares the same calculation engine used throughout EleCalculator but is configured specifically for first-order RC networks. It assumes linear components operating within their voltage, current, and temperature ratings.
1. Select what you want to solve
- Time Constant – Computes τ = R × C and key charging points (63.2%, 90%, ~99%). Suitable for delay networks and simple timing circuits.
- Frequency Response / Impedance Analysis – Uses Xc = 1/(2πfC) and Z = √(R² + Xc²) for series RC, or the corresponding parallel form, plus phase angle.
- Filter Design – Uses either a target cutoff frequency fc or time constant τ to recommend R–C pairs for low-pass or high-pass behaviour.
- Transient Analysis – Reports capacitor voltage at standard multiples of τ for a given step voltage.
2. Enter resistance, capacitance, and operating point
- Enter resistance R in ohms (Ω) and capacitance C in microfarads (μF). The tool internally converts C to farads.
- For time-domain work, provide the applied step voltage in volts so the calculator can report absolute capacitor voltage at each τ.
- For AC and filter work, provide frequency in hertz (Hz) when analysing a specific operating point.
3. Interpret time-constant and step-response results
| Quantity | Formula | Typical interpretation |
|---|---|---|
| Time constant | τ = R × C | Time for Vc to reach ≈63.2% of a step input in an ideal RC. |
| Charging curve | Vc(t) = Vstep(1 − e−t/τ) | Use 1τ, 3τ, and 5τ as practical reference points for timing design. |
| Discharging curve | Vc(t) = V0e−t/τ | Applies to bleed-down networks and snubber discharge intervals. |
4. Use frequency-domain results for filter work
| Quantity | Formula | Notes |
|---|---|---|
| Capacitive reactance | Xc = 1/(2πfC) | Magnitude of capacitor impedance vs frequency. |
| Cutoff frequency | fc = 1/(2πRC) | −3 dB point for simple RC low-pass or high-pass networks. |
5. When to use related tools
- For full complex impedance and mixed R–L–C work, use the impedance calculator.
- For choosing practical capacitor values and packages, see the capacitor calculator and capacitor code calculator.
- For circuit-level context on how R and C appear in networks, refer to the series and parallel circuits guide and Kirchhoff's Laws guide.
Common Applications
More applications. Open to review 2 additional use cases.
Frequently Asked Questions
How do I calculate the RC time constant and charging curve?
For a first-order RC network, the time constant is τ = R × C (with C in farads). For a step from 0 to V_step, the capacitor voltage is Vc(t) = V_step(1 − e^(−t/τ)). The tool reports τ, τ in milliseconds, and typical reference points such as 63.2%, 90%, and ≈99% of the final value so you can relate abstract formulas to practical delays.
What assumptions does this RC circuit calculator make?
The calculator assumes a linear, first-order RC network with ideal components at the specified operating point. It does not model dielectric absorption, ESR, ESL, non-linear capacitance, or detailed stray impedances. For AC analysis it treats R and C as lumped elements and uses Xc = 1/(2πfC) with series or parallel combinations. Final designs should always be checked against device datasheets and, where applicable, standards such as NFPA 70 (NEC) or relevant manufacturer documents.
Can I use this tool for mains-level motor starters and snubber design?
The results are suitable for first-pass sizing and concept checks, for example estimating τ or f_c before selecting specific RC components. For mains-level motor starters, snubbers, or power-electronics work, you must still follow manufacturer application notes, insulation and creepage/clearance requirements, and applicable electrical codes. Treat the calculator output as numerical support, not as a standalone design or approval step.
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