What this calculator does
Capacitors combine in the opposite way to resistors, which is the thing that catches people out. In parallel their capacitances simply add; in series the total drops below the smallest one in the group.
The reason is physical rather than arbitrary. Connecting capacitors in parallel effectively enlarges the plate area, which stores more charge. Connecting them in series stacks the dielectric gaps, which makes the combination harder to charge.
The formula
For parallel, add the capacitances. For series, add the reciprocals and take the reciprocal of the total. Leave the third and fourth values at zero to work with a pair.
| Term | Meaning |
|---|---|
| Farad (F) | The unit of capacitance: one coulomb stored per volt. Practical capacitors are usually microfarads or smaller. |
| Parallel | Capacitors connected across the same two points. Capacitances add. |
| Series | Capacitors connected one after another. Reciprocals add, so the total falls. |
The inputs explained
| Field | What to enter |
|---|---|
| C1 (µF) | The first capacitance, in microfarads. |
| C2 (µF) | The second capacitance, in microfarads. |
| C3 (0 to ignore) (µF) | A third capacitance if present. Leave at zero to ignore. |
| C4 (0 to ignore) (µF) | A fourth capacitance if present. Leave at zero to ignore. |
When to use it
Making up a value you do not stock
Standard capacitor values are coarse, and combining two in parallel is the usual way to hit an awkward figure.
Raising the working voltage
Capacitors in series divide the applied voltage between them, which is one way to handle a voltage above any single part's rating.
Increasing bulk storage
Parallel capacitors add capacitance directly, which is how large smoothing banks are built from smaller units.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How do series and parallel totals compare for a 10 µF capacitor paired with another?
A 10 microfarad capacitor paired with a range of second values.
| C2 | Parallel total | Series total |
|---|---|---|
| 10 µF | 20.000 µF | 5.000 µF |
| 22 µF | 32.000 µF | 6.875 µF |
| 47 µF | 57.000 µF | 8.246 µF |
| 100 µF | 110.000 µF | 9.091 µF |
Questions
Why is this the opposite of resistors?
Because capacitance measures charge stored per volt rather than opposition to current. Adding capacitors in parallel adds plate area and therefore storage, while resistors in parallel add current paths and therefore reduce resistance.
Why would anyone put capacitors in series?
Mainly to share voltage. Two 400 V capacitors in series can handle 800 V, at the cost of halving the capacitance. Balancing resistors are usually fitted alongside to ensure the voltage divides evenly.
Does the voltage rating change?
In series the applied voltage divides between the capacitors, so the combination withstands more. In parallel every capacitor sees the full voltage, so the combination is limited by the lowest-rated part.
What about the charge stored?
In series every capacitor carries the same charge, while the voltages differ. In parallel every capacitor sees the same voltage, while the charges differ. This is the mirror image of how current and voltage behave with resistors.
For the resistor equivalent, see the resistors in series and parallel calculator. For the energy a capacitor stores, see the capacitor charge and energy calculator.