How to Calculate Series and Parallel Capacitors
Capacitors behave the opposite of resistors. Capacitors in parallel add up: C = C1 + C2 + … (the value increases). In series 1/C = 1/C1 + 1/C2 + … (the value decreases); for two capacitors C = (C1 × C2) / (C1 + C2). For example, two 10 µF capacitors give 20 µF in parallel and 5 µF in series.
When you wire capacitors in series or parallel, the formulas are the exact opposite of resistors: a parallel connection increases the total capacitance, a series connection decreases it. Once you grasp this reversal the calculations become easy.
Parallel capacitors: the values add up
In a parallel connection the same voltage is applied to every capacitor and the stored charges add. So the total capacitance is the sum of the individual values:
Ctotal = C1 + C2 + … + Cn
The result is always larger than the biggest capacitor. To increase capacitance (for example in a power-supply filter) capacitors are wired in parallel.
Series capacitors: reciprocals decrease the value
In a series connection the same charge flows through every capacitor and the voltage is shared inversely with their values. The total capacitance is the reciprocal of the sum of reciprocals:
1 / Ctotal = 1/C1 + 1/C2 + … + 1/Cn
The result is always smaller than the smallest capacitor. Shortcuts:
| Case | Shortcut |
|---|---|
| Two capacitors (C1, C2) | C = (C1 × C2) / (C1 + C2) |
| n EQUAL capacitors (C) | Ctotal = C / n |
Why the opposite of resistors?
The difference comes from the physics of capacitance: capacitance grows with plate area. Wiring capacitors in parallel is like placing the plates side by side to enlarge the total area → capacitance rises. Wiring them in series effectively increases the dielectric gap (plate spacing) → capacitance falls. In a resistor, flow resists passage; in a capacitor, storage depends on geometry — which is why the formulas swap.
Resistor or capacitor? Direction comparison
| Connection | Resistor | Capacitor |
|---|---|---|
| Series | Adds up (increases) | Reciprocals (decreases) |
| Parallel | Reciprocals (decreases) | Adds up (increases) |
Worked examples
- Parallel: 10 µF + 10 µF = 20 µF.
- Series (equal): 10 µF ‖ 10 µF (series) = 10 / 2 = 5 µF.
- Series (unequal): 4.7 µF with 10 µF in series = (4.7 × 10) / (4.7 + 10) = 47 / 14.7 ≈ 3.2 µF.
Common mistakes
- Applying the resistor formula to capacitors: the direction is reversed — add in parallel, reciprocals in series.
- Ignoring the voltage rating: a series connection shares the voltage but not equally; the smallest capacitor sees the highest voltage.
- Mixing up polarity on polarized capacitors: place the polarity correctly when wiring electrolytic capacitors in series or parallel.
Use the calculator
To enter several capacitors in series or parallel and get the equivalent capacitance instantly, use our Parallel/Series Capacitor Calculator.