Series and parallel capacitance — the mirror of resistors
Capacitors combine the opposite way to resistors. In parallel, the plate areas effectively add, so capacitances add: Ctotal = C₁ + C₂ + … — the total is larger than any one.
In series, the same charge sits on every capacitor but the voltages add, so the reciprocals add: 1/Ctotal = 1/C₁ + 1/C₂ + … — the total is smaller than the smallest capacitor. For two in series the shortcut is Ctotal = (C₁ × C₂) / (C₁ + C₂), and N equal capacitors in series give C/N.
Worked examples
Parallel: 100 nF ∥ 220 nF ∥ 1 µF = 1.32 µF.
Series: 100 nF and 220 nF in series: (100 × 220) / (100 + 220) ≈ 68.75 nF — smaller than either, as expected.
Why put capacitors in series?
Two reasons come up in practice:
- Higher voltage. Series capacitors share the applied voltage, so a string withstands more than any single part — common in high-voltage supplies (add balancing resistors so the voltage divides evenly).
- A value you don't stock. Series and parallel combinations let you hit a capacitance between standard values.
Frequently asked questions
- Does voltage rating add in series?
- Ideally the string's rating is the sum, but only if the voltage divides evenly — mismatched leakage can unbalance it. Balancing resistors across each capacitor keep the split even and bleed the charge down safely.
- What about parallel voltage rating?
- In parallel every capacitor sees the full voltage, so the bank's rating is that of the lowest-rated part. The capacitances add; the voltage rating does not.
- Which standard series do capacitors use?
- Usually the coarser E-series — E3, E6, or E12 — so the calculator shows the nearest E12 value. Precision film capacitors can be tighter.
- Need resistors instead?
- The series & parallel resistor calculator does the mirror-image math, plus a standard-value combination solver.