Free capacitor calculator
Combine capacitors in series or parallel and get the equivalent capacitance — remembering caps add the opposite way to resistors — updated live, as you type.
On this page14 sections
Parallel: C = C1 + C2 + … Series: 1/C = 1/C1 + 1/C2 + … (inverse of resistors).
Results are estimates. Consult a professional.
How the capacitor calculator works
This capacitor calculator combines two or more capacitors wired in series or in parallel and reports the single equivalent capacitance the network behaves as. The one fact to anchor on is that capacitors combine the opposite way to resistors: in parallel their values add directly, while in series the reciprocals add, so the series total is always smaller than the smallest capacitor in the chain. Enter each capacitance, pick the arrangement, and the calculator returns the total in the same unit you used.
Why capacitors combine the opposite way to resistors
Almost everyone who has used a resistor calculator first reaches for the wrong rule with capacitors, because the behaviour is reversed. The reason comes straight from what a capacitor is: two conducting plates separated by an insulating dielectric. Capacitance grows with plate area and shrinks as the gap between the plates gets thicker.
Parallel capacitors — a bigger plate
Wiring capacitors in parallel connects all their plates side by side, which is electrically the same as building one capacitor with a larger total plate area. More area means more capacitance, so the values simply add. Two 10 µF capacitors in parallel behave as a single 20 µF capacitor.
Series capacitors — a thicker dielectric
Wiring capacitors in series stacks their dielectrics end to end, which is like building one capacitor with a thicker gap between the plates. A thicker gap means less capacitance, so the total drops below the smallest capacitor in the string. The same charge has to push across every dielectric in turn, which is why the reciprocals add.
If you are coming from the resistive side of a design, the companion resistor (series / parallel) calculator uses the swapped rules — series resistors add, parallel resistors reciprocate — so the two tools are mirror images of each other.
Worked example — capacitors in parallel
Sam is building a power-supply smoothing bank and wants the largest practical bulk capacitance from three parts on the bench: 10 µF, 22 µF and 47 µF. Wiring them in parallel gives the most capacitance.
Step 1 — Use the parallel rule (just add)
C = C1 + C2 + C3 = 10 + 22 + 47 = 79 µF. Because the values add directly, no unit conversion or reciprocals are needed — keep everything in microfarads and sum.
Parallel is the arrangement you reach for when you want bulk capacitance, more energy storage, or to reach an odd value (say 79 µF) that no single standard part provides.
Worked example — capacitors in series
Now Sam wires the identical three capacitors — 10 µF, 22 µF and 47 µF — in series instead, to see how different the result is.
Step 1 — Add the reciprocals
1/C = 1/10 + 1/22 + 1/47 = 0.10000 + 0.04545 + 0.02128 = 0.16673 per µF.
Step 2 — Invert to get the total
C = 1 ÷ 0.16673 = 5.9977 µF — smaller than the smallest capacitor in the string (10 µF), and far below the 79 µF the same parts gave in parallel.
For just two capacitors the reciprocal rule simplifies to the product-over-sum form C = (C1 × C2) / (C1 + C2). For example, a 100 pF and a 220 pF capacitor in series give 100 × 220 / (100 + 220) = 68.75 pF.
Capacitor combination and unit quick-reference
The first table shows how the same set of capacitors gives very different totals depending on the wiring. The second is the unit ladder you need when a network mixes microfarads, nanofarads and picofarads — convert everything to one unit before combining.
| Capacitors | In parallel (add) | In series (reciprocal) |
|---|---|---|
| 10 µF + 10 µF | 20 µF | 5 µF |
| 100 nF + 100 nF | 200 nF | 50 nF |
| 10 µF + 22 µF + 47 µF | 79 µF | 5.9977 µF |
| 100 pF + 220 pF | 320 pF | 68.75 pF |
| 1 µF + 1 µF + 1 µF | 3 µF | 0.333 µF |
Computed from C = C1 + C2 + … (parallel) and 1/C = 1/C1 + 1/C2 + … (series). Note how series totals always fall below the smallest part while parallel totals rise above the largest.
| Unit | Symbol | In farads | Conversions |
|---|---|---|---|
| Microfarad | µF | 1×10⁻⁶ F | 1 µF = 1,000 nF = 1,000,000 pF |
| Nanofarad | nF | 1×10⁻⁹ F | 1 nF = 0.001 µF = 1,000 pF |
| Picofarad | pF | 1×10⁻¹² F | 1 pF = 0.001 nF = 0.000001 µF |
Capacitor markings use these three units almost exclusively. To combine mixed sizes, convert them all to the smallest unit first, then apply the series or parallel rule.
Voltage ratings in series and parallel
Capacitance is only half the story — every capacitor also has a maximum voltage rating, and series and parallel treat that voltage in opposite ways. Getting this wrong is the fastest way to destroy a capacitor.
Parallel shares the voltage
Capacitors in parallel all sit across the same two nodes, so they share the full applied voltage equally. Each capacitor must be rated for that whole voltage; the rating of the bank is the rating of its lowest-rated member. Parallel does not buy you a higher voltage rating.
Series splits the voltage
Capacitors in series divide the applied voltage between them, which is sometimes used to reach a higher working voltage than any single part allows. The catch is that the split is inversely proportional to capacitance: the smallest capacitor sees the largest share of the voltage. Mismatched values or leakage currents can push one capacitor past its rating.
Where series and parallel capacitors are used
Designers pick the arrangement by what they need: more capacitance and energy storage, or a higher voltage rating and a precise non-standard value.
- Bulk smoothing (parallel) — power-supply rails use large electrolytic capacitors in parallel to store charge and hold the voltage steady under load.
- Decoupling and bypass (parallel) — a small ceramic capacitor sits in parallel next to each chip to supply fast current spikes the bulk capacitor is too slow to deliver.
- Higher voltage strings (series) — series stacks reach a working voltage no single capacitor in the kit can survive, common in high-voltage supplies.
- Fine-tuning a value (series or parallel) — parallel reaches an odd larger value; series trims down to a precise smaller value than stock parts provide.
- Tuned circuits — the equivalent capacitance you compute here feeds straight into a resonant-frequency calculation.
Once you have the total capacitance, the resonant frequency (LC) calculator turns it into a tuning frequency, and Ohm's law covers the voltage, current and power elsewhere in the circuit.
Common mistakes and capacitor tolerance
- Using the resistor rules. The single most common error: adding in series and reciprocating in parallel. Capacitors do the opposite — add in parallel, reciprocate in series.
- Forgetting series is smaller. If your series total is larger than the smallest capacitor, the math is wrong. Series always lands below the smallest part.
- Mixing units. Combining 100 pF with 0.1 µF without converting gives nonsense. Put everything in one unit first.
- Ignoring the voltage rating. A correct capacitance with an under-rated capacitor still fails. Check the rating for the arrangement, not just the value.
Real capacitors also carry tolerance. Film and ceramic Class 1 (C0G/NP0) parts are typically ±1% to ±10%; general ceramic and electrolytic parts run ±20% or worse, and Class 2 ceramics lose capacitance with applied DC voltage and age. So a network you calculate as 79 µF may measure anywhere across a wide band. Designers commonly derate electrolytic capacitors — running them well below their rated voltage — to extend life, and treat the calculated value as a nominal target. For the combination derivation and tolerance background, see Wikipedia's capacitor reference and HyperPhysics' "Capacitor Combinations" page (Georgia State University).
Capacitor combination definitions
How accurate is this capacitor calculator
The arithmetic is exact. For the capacitances you enter, C = C1 + C2 + … (parallel) and 1/C = 1/C1 + 1/C2 + … (series) are the precise equivalent capacitance of ideal capacitors, computed to full floating-point precision.
Real parts deviate for physical reasons, not arithmetic ones. Manufacturing tolerance, voltage and temperature coefficients, ageing, leakage and the equivalent series resistance of each capacitor all shift the measured value away from the nominal one. Treat the calculated number as the design target, confirm it with a capacitance meter on the bench, and always check the voltage rating for the arrangement you have chosen.
Frequently asked questions about the free capacitor calculator
About this Capacitor (series / parallel) calculator
This capacitor calculator runs entirely in your browser, with nothing sent to a server. Enter two or more capacitor values, choose series or parallel, and it returns the single equivalent capacitance the network behaves as. Capacitors combine the opposite way to resistors — parallel values add directly, while series values combine reciprocally and always total less than the smallest capacitor — so the tool applies the right rule for the arrangement you pick and keeps your units consistent.