Capacitor Series Calculator
Capacitors wired in series share the same charge but split the voltage, which makes the combination store less charge per volt than any single capacitor.
Enter Values
How to use this calculator
- Enter the value of each capacitor in microfarads (µF). Convert first if needed: 1 nF = 0.001 µF, 1 pF = 0.000001 µF.
- Fill Capacitor 1 and Capacitor 2; add a third value only if your string has three capacitors (leave it blank or 0 otherwise).
- Read the total (equivalent) series capacitance in µF and nF, and open the steps to see the reciprocal-sum working.
How it works
Capacitors wired in series share the same charge but split the voltage, which makes the combination store less charge per volt than any single capacitor. The equivalent capacitance is found from the reciprocal-sum rule: 1/Ct = 1/C1 + 1/C2 + 1/C3 + …, then Ct = 1 divided by that sum. This is the same maths used for resistors in parallel — the roles are simply swapped.
Because every 1/C term is positive, the reciprocal sum is always larger than any individual 1/C, so the total capacitance Ct is always smaller than the smallest capacitor in the string. For two capacitors the rule simplifies to the product-over-sum form Ct = (C1 × C2) / (C1 + C2). All values here are entered in microfarads (µF); the tool also reports the result in nanofarads (nF) for convenience.
Worked example
Two capacitors in series. Put a 10 µF and a 22 µF capacitor in series. 1/Ct = 1/10 + 1/22 = 0.145454… per µF, so Ct = 1 / 0.145454… = 6.875 µF (6,875 nF). As expected, the series total (6.875 µF) is smaller than the smaller capacitor (10 µF).
Common mistakes
- Adding the capacitances like resistors in series — series capacitors do NOT simply add; you must use the reciprocal (1/C) rule, which gives a smaller total.
- Mixing units. Enter every value in the same unit (µF here). A stray nF or pF value typed as if it were µF will be off by a factor of a thousand or a million.
- Expecting the total to be bigger than the parts. In series the equivalent capacitance is always less than the smallest capacitor — if your answer is larger, you have used the parallel rule by mistake.
Frequently asked questions
Why is series capacitance smaller than the smallest capacitor?
In series the same charge sits on each capacitor, but the applied voltage is shared between them, so the string needs more volts to hold the same charge. Storing less charge per volt means a lower capacitance — mathematically the reciprocal sum guarantees Ct is below every individual value.
How is this different from capacitors in parallel?
Parallel capacitors simply add (Ct = C1 + C2 + …) and the total is larger than any single one. Series capacitors use the reciprocal-sum rule and the total is smaller. Series capacitance behaves like parallel resistance, and vice versa.
What about the voltage rating of a series string?
Combining capacitors in series raises the total voltage the string can withstand (the applied voltage divides across them), which is one reason series wiring is used. This calculator returns the equivalent capacitance only, not the voltage split, which depends on each capacitor's value and tolerance.
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