Capacitor Series & Parallel Calculator
Combine any number of capacitors in series or parallel — parallel adds, series uses the reciprocal sum — with SI-prefix input.
Combining capacitors
Capacitors combine the opposite way to resistors.In parallel the plate areas effectively add, so the capacitances add. In series the reciprocals add, giving a total smaller than the smallest capacitor.
Parallel: C = C₁ + C₂ + … + Cₙ
Series: 1/C = 1/C₁ + 1/C₂ + … + 1/Cₙ
For two capacitors in series this is the "product over sum" rule: C = C₁·C₂ / (C₁ + C₂). Two equal capacitors in series give half the value.
Why capacitors are the opposite of resistors
A capacitor stores charge on two plates, and its capacitance grows with plate area. Wire two in parallel and you've effectively made one bigger plate pair, so the values add. Put them in series and the same charge has to cross both, which is like stacking the plate gaps — the combined capacitance falls below the smallest one, following the reciprocal rule. It's exactly the reverse of how resistors behave, which trips up almost everyone at first.
Worked example
Two 100 nF capacitors in parallel make 200 nF. The same two in series make 1/C = 1/100 + 1/100, so C = 50 nF — half the value. For unequal parts, the product-over-sum shortcut works for two in series: a 100 nF and a 220 nF give 100·220 / (100 + 220) ≈ 68.75 nF.
Where each is used
Parallel capacitors are common for bulk plus high-frequency decoupling — a large electrolytic alongside a small ceramic covers both slow and fast current demands. Series capacitors split voltage, so two lower-voltage parts can share a higher rail, and they let you reach a non-standard value. Working with a resistor and capacitor together? See theRC time constant calculator.
Common questions
- Why do capacitors combine the opposite way to resistors?
- Because capacitance measures how much charge a component stores per volt, and putting capacitors side by side gives the charge more places to go. So parallel capacitors add (C₁ + C₂), exactly like resistors in series, and series capacitors combine reciprocally, like resistors in parallel. It catches people out constantly, so it is worth checking your answer against the rule of thumb below.
- What is a quick sanity check on the answer?
- Series always gives you less than the smallest capacitor in the chain; parallel always gives more than the largest. If your series result is bigger than any individual value, you have used the parallel formula by mistake. Two equal capacitors in series give exactly half; in parallel, exactly double.
- Why would anyone put capacitors in series?
- Mainly for voltage rating. Series capacitors share the applied voltage, so two 400 V parts can handle 800 V where one could not — at the cost of halving the capacitance. The catch is that they only share the voltage equally if their leakage matches, which is why series electrolytics are usually fitted with balancing resistors across each one.
- Do tolerances matter much here?
- More than with resistors, yes. Electrolytics are commonly ±20% and can be −10%/+50%, and ceramics of class 2 dielectric lose a substantial fraction of their rated value under DC bias — a 10 µF X5R part can behave as 5 µF at its rated voltage. So treat a computed total as nominal, and where the value genuinely matters use a film or C0G part whose tolerance is tight and stable.