Capacitor Calculator
Calculate capacitance, stored energy, RC timing, equivalent capacitor networks, and AC capacitor size from the electrical values you already know.
Calculate capacitor values in three steps
The calculator converts every input to base SI units, applies the correct electrical relationship, and then displays the result in a practical capacitor unit such as µF, nF, or pF.
1. Select a method
Choose charge, energy, RC timing, a series/parallel network, or AC reactive-power sizing.
2. Enter known values
Use the unit selectors beside each field. The tool converts units automatically before calculating.
3. Review the result
Check the primary value, supporting electrical values, formula, substitution, and engineering note.
Capacitor formulas used by this tool
C = Q ÷ VCapacitance equals stored charge divided by the voltage across the capacitor.
E = ½CV²Energy increases linearly with capacitance and with the square of voltage.
τ = RCOne time constant represents about 63.2% charging or 36.8% remaining during discharge.
fc = 1 ÷ (2πRC)The -3 dB cutoff of an ideal first-order RC filter.
Ceq = C₁ + C₂ + …Parallel capacitances add because each capacitor has the same voltage.
1/Ceq = Σ(1/C)Series networks share charge and produce an equivalent value below the smallest capacitor.
Common capacitor unit conversions
| Unit | Symbol | Value in farads | Typical use |
|---|---|---|---|
| Farad | F | 1 F | Supercapacitors and energy storage |
| Millifarad | mF | 10⁻³ F | Large power-supply filtering |
| Microfarad | µF | 10⁻⁶ F | Power supplies, motors, audio circuits |
| Nanofarad | nF | 10⁻⁹ F | Timing, filtering, signal coupling |
| Picofarad | pF | 10⁻¹² F | RF, oscillators, high-frequency tuning |
Capacitor calculator FAQs
What does capacitance measure?
Capacitance measures how much electric charge a component stores per volt. One farad equals one coulomb of charge per volt.
How do I calculate capacitor energy?
Use E = ½CV², where E is joules, C is farads, and V is volts. Because voltage is squared, a voltage increase has a strong effect on stored energy.
What is an RC time constant?
The RC time constant is resistance multiplied by capacitance. After one time constant, an ideal charging capacitor reaches approximately 63.2% of its final voltage.
Do capacitors add in series or parallel?
Parallel capacitances add directly. Series capacitances combine reciprocally, so the equivalent series value is always lower than the smallest individual capacitor.
Can I use the exact calculated capacitor value?
Real capacitors come in preferred standard values and have tolerances. Select a suitable standard value and check voltage rating, ESR, ripple current, temperature rating, dielectric type, and physical size.
Can this calculator design a power-factor capacitor bank?
The AC mode provides an ideal fundamental-frequency capacitance estimate from kVAR, voltage, frequency, and connection. Final bank design requires harmonic, resonance, switching, discharge, protection, and standards assessment by a qualified professional.
What voltage rating should a capacitor have?
The rated voltage must exceed the maximum voltage the capacitor will experience, including ripple, transients, tolerances, and applicable design margin. Use component and equipment standards for the final selection.