Capacitor Calculator Guide
A capacitor calculator computes relationships among capacitance (C), voltage (V), charge (Q), energy (E), reactance (Xc), and RC time constants. It also solves series/parallel combinations for design and troubleshooting.
What is Capacitor Calculator?
The capacitor calculator helps engineers and hobbyists size components for filters, power supplies, timing circuits, and coupling/decoupling. It supports SI units, unit prefixes, and multiple sub-calculations.
How to Use the Capacitor Calculator
- Choose a mode: Q/C/V, Energy, Reactance, RC timing, or Series/Parallel.
- Enter known values with units (F, uF, nF; Hz; Ohms).
- Calculate the unknown; convert units as needed.
- Check ratings (voltage, ESR, ripple) for real components.
- Iterate for "what-ifs" (frequency shifts, different R/C values).
Formulas & Methods
- Charge:
Q = C·V - Energy:
E = 1/2·C·V^2 - Reactance:
Xc = 1/(2πfC) - RC charging:
V(t) = Vs·(1 - e^(−t/RC)); discharging:V(t) = V0·e^(−t/RC) - Cutoff (single-pole):
f_c = 1/(2πRC) - Combinations:
- Parallel:
C_T = Σ C_i - Series:
1/C_T = Σ (1/C_i)
- Parallel:
Assumptions & limitations
- Ideal components; real capacitors have ESR, leakage, voltage-dependent C, and tolerance.
- High-frequency behavior requires impedance models beyond Xc.
- Observe polarity for electrolytics and derate voltage for reliability.
Examples
Example A — Reactance at audio
C = 100 nF, f = 1 kHz → Xc = 1/(2π·1e3·1e−7) ≈ 1,592 Ω.
Example B — RC timing
R = 47 kΩ, C = 10 uF → τ = 0.47 s; ~63% charge in 1τ, ~99% in 5τ.
| Task | Formula | Result |
|---|---|---:|
| Stored energy | 1/2·C·V^2 | 470 uF @ 16 V → 0.060 J |
| Series combo | 1/C_T = Σ1/C | 10 uF || 10 uF → 5 uF |
Pro Tips & Best Practices
- Derate voltage (e.g., use ≤50–70% of rated V) for longevity.
- Choose dielectric to match need (C0G/NP0 for stability, X7R for density, electrolytic for bulk).
- Check ESR and ripple current for power rails.
- Use film caps for audio paths when low distortion matters.
- Account for tolerance (±5%, ±10%, etc.) in sensitive filters.
Related Calculators
FAQ
Q: How do I calculate capacitor charge and energy?
A: Use Q = C·V for charge and E = 1/2·C·V^2 for stored energy.
Q: What is capacitive reactance?
A: Xc = 1/(2πfC) describes a capacitor’s opposition to AC; it decreases as frequency increases.
Q: How do capacitors combine?
A: In parallel: C_total = ΣC. In series: 1/C_total = Σ(1/C).
Q: What is the RC time constant?
A: τ = R·C; it sets the speed of charge/discharge: V(t) = Vs·(1 - e^(−t/RC)) for charging.
Q: Any safety considerations?
A: Respect voltage ratings and discharge capacitors before handling; high-voltage capacitors can retain a dangerous charge.
Engineering note: SI units assumed; steady-state AC formulas use radians/second internally for ω = 2πf when appropriate.
Call to Action
Plug in your values to size capacitors, check reactance, and estimate timing—then iterate with series/parallel combos to hit targets cleanly.