This series and parallel capacitor calculator finds the equivalent capacitance of up to six capacitors — and the rules are the mirror image of resistors: parallel adds directly, series uses reciprocals.
| Equivalent capacitance | – |
| Stored energy at bank voltage | – |
| Stored charge | – |
Capacitors Vote the Opposite Way From Resistors
Single-cap physics (C = Q/V, plate geometry) is our Capacitance Calculator. Part of our Physics Calculators collection.
Worked Examples (Verified)
- 10 µF + 20 µF in parallel (defaults): C = 30 µF — at 12 V storing Q = 360 µC and E = ½CV² = 2.16 mJ
- The same pair in series: 1/C = 1/10 + 1/20 → C = 6.67 µF — below the smaller capacitor, exactly the resistor-parallel pattern; the mnemonic is “capacitors follow the OTHER component’s rule”
- Why series shrinks C: the stack behaves like one capacitor with a thicker dielectric (gaps add), while parallel stacks plates side by side (areas add) — geometry explains both formulas
Circuit Discipline
- Series voltage warning: voltage divides inversely with C in series — the SMALLEST capacitor takes the LARGEST voltage share; mismatched series banks need balancing resistors in real high-voltage work.
- Series charge is identical on every capacitor (the middle plates form an isolated island) — that’s the derivation’s engine.
- Electrolytic polarity: parallel banks keep polarity aligned; a reversed electrolytic in the bank is a small chemical event waiting for power-up.
- Tolerance stacking: ±20% parts make exact equivalents fuzzy — design with the tolerance band, not the label.
Related Tools
- Capacitance Calculator — C from charge, voltage, geometry
- Series & Parallel Resistor Calculator — the mirror rules
- Physics Calculators — the full collection
Frequently Asked Questions
How do you calculate capacitors in parallel?
Add them: C = C₁ + C₂ + …. Physically the plates’ areas combine. Example: 10 + 20 = 30 µF. Parallel is the easy direction for capacitors — opposite of resistors.
How do you calculate capacitors in series?
By reciprocals: 1/C = 1/C₁ + 1/C₂ + …, then invert — 10 µF and 20 µF in series give 6.67 µF, smaller than either. For two: C = (C₁C₂)/(C₁ + C₂), the same “product over sum” as parallel resistors.
Why do the capacitor rules mirror the resistor rules?
Because C = Q/V behaves like a conductance-style quantity: capacitors in parallel share voltage and sum charge (like parallel conductances), while in series they share charge and sum voltages (like series resistances). The physics is plate geometry; the algebra follows from what’s shared.
How much energy does a capacitor bank store?
E = ½ Ceq V² with the bank’s equivalent C. The default 30 µF at 12 V: 2.16 mJ. Note the V² — doubling voltage quadruples stored energy (and stress), the quickest sanity check on any bank design.
Can series capacitors share voltage unevenly?
Yes — voltage divides in inverse proportion to capacitance (same charge Q, V = Q/C), so the smallest C takes the biggest V. It can exceed that part’s rating even when the bank total looks safe; high-voltage series strings use balancing resistors for exactly this reason.
Is this capacitor calculator free?
Yes — free, instant, no sign-up.