Series Capacitance Calculator
Enter two capacitor values and get their combined capacitance in series — the single number behind voltage dividers, higher voltage ratings, and tuned circuits.
Two values, one answer
Enter both capacitor values in farads and the calculator returns the series total with the product-over-sum rule, C = (C1 × C2) ÷ (C1 + C2).
Always smaller
The series total is always smaller than the smaller of your two capacitors — wiring them end to end increases the effective plate separation.
What does series capacitance mean?
Two capacitors, one combined value
Two capacitors are wired in series when they sit end to end so the same charge flows through both. Together they behave like a single capacitor whose value you get from the product-over-sum rule, written C = (C1 × C2) ÷ (C1 + C2). Capacitors in series combine exactly like resistors in parallel — the same shortcut, applied to capacitance instead of resistance. Because connecting them end to end increases the effective distance between the outer plates, the pair always stores less charge per volt, so the combined value is smaller than either capacitor on its own. That is the opposite of a parallel connection, where capacitors share both ends and you simply add them.
Enter both capacitances in farads to get the combined series capacitance instantly.
One short formula, built from the two capacitor values C1 and C2.
C = (C1 × C2) ÷ (C1 + C2)Multiply the two capacitances to get the product, add them to get the sum, then divide the product by the sum. The "product over sum" shortcut is the two-capacitor case of the more general series rule (1 ÷ C = 1 ÷ C1 + 1 ÷ C2); for exactly two capacitors it is the quickest form to work by hand.
Suppose you wire a 2 F capacitor in series with a 3 F capacitor.
Product
2 × 3 = 6 — multiply the two capacitances together.
Sum
2 + 3 = 5 — add the two capacitances together.
Divide
6 ÷ 5 = 1.2 F — the combined series capacitance, smaller than either one.
The combined value tells you how the pair behaves as a single capacitor, and the first thing to notice is that it is always smaller than the smaller of your two capacitors. That is not a quirk of the formula — it is the physics. Stacking capacitors end to end increases the effective separation between the outer plates, and capacitance drops as the plates move apart, so the combination stores less charge per volt. Two equal capacitors are the easy case: the series total is exactly half of one of them, which is why 4 F and 4 F give 2 F, and 10 F with 10 F give 5 F. When the two values differ, the result leans toward the smaller one — a 2 F capacitor in series with a 3 F capacitor gives 1.2 F, closer to 2 than to 3. There is a useful payoff for that smaller value: in series the applied voltage splits across each capacitor, so the combination can handle a higher total voltage than a single capacitor could. This is the exact opposite of a parallel connection, where capacitances add and the total grows.
The product-over-sum rule is exact for two ideal capacitors, but a couple of practical points are worth keeping in mind.
Two capacitors, ideal and in the same unit
This calculator combines exactly two capacitors. For three or more in series, apply the rule in stages (combine the first two, then put the result in series with the third) or use the general reciprocal form. Keep both values in the same unit — farads here — and remember the formula assumes ideal capacitors; real components carry a tolerance, leakage, and equivalent series resistance, and the voltage rating splits according to each capacitor's value, not evenly.