Capacitor Calculator
Calculate charge, energy, and RC time constant for a capacitor, or find the total capacitance of series and parallel combinations.
Stored charge (Q)
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Stored energy (E)
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Enter capacitor values to find series and parallel totals.
Parallel total
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Series total
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Time constant (τ)
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Fully charged (5τ)
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| Time | Charge % | Voltage % of V_s |
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Capacitor Formulas
Charge and Energy
$$Q = C \times V \qquad E = \frac{1}{2} C V^2$$
Where Q is charge in coulombs (C), C is capacitance in farads (F), V is voltage, and E is energy in joules (J).
Series and Parallel Combinations
Parallel (capacitances add — opposite of resistors):
$$C_{total} = C_1 + C_2 + C_3 + \ldots$$
Series (reciprocals add — like parallel resistors):
$$\frac{1}{C_{total}} = \frac{1}{C_1} + \frac{1}{C_2} + \frac{1}{C_3} + \ldots$$
RC Time Constant
$$\tau = R \times C$$
One time constant is the time for the capacitor to charge to 63.2% of the supply voltage (or discharge to 36.8%). Five time constants (5τ) is considered "fully charged" (99.3%).
Capacitor Types
| Type | Typical range | Polarity | Use |
|---|---|---|---|
| Ceramic (MLCC) | 1 pF – 100 µF | Non-polar | Decoupling, filtering |
| Film (polyester, polypropylene) | 1 nF – 100 µF | Non-polar | AC circuits, precision timing |
| Electrolytic (aluminium) | 1 µF – 100,000 µF | Polar | Power supply filtering, bulk storage |
| Tantalum | 0.1 µF – 2,200 µF | Polar | Low-profile, low-ESR applications |
| Supercapacitor (ultracap) | 0.1 F – 3,000 F | Non-polar | Energy storage, backup power |
Frequently Asked Questions
What does capacitance mean in practical terms?
Capacitance measures how much charge a capacitor stores per volt. A 1 µF capacitor charged to 5 V stores Q = 1×10⁻⁶ × 5 = 5 µC of charge. Larger capacitance means more energy stored at the same voltage — useful for power supply filtering (smoothing voltage ripple) and timing circuits.
Why do capacitors in series have less total capacitance?
In a series string, the same charge must appear on each capacitor's plates. The voltage distributes across them inversely to their capacitance. The result is a lower total capacitance, but the string can handle higher total voltage.
Can a capacitor replace a battery?
Supercapacitors can store significant energy, but standard capacitors store far less energy per unit volume than batteries. A 10,000 µF capacitor charged to 5 V stores only E = ½ × 0.01 × 25 = 0.125 J — enough to flash an LED for a fraction of a second. They are used for short backup bursts, not sustained operation.
