Capacitor Series Value Calculator

A series capacitor circuit produces an equivalent capacitance that is lower than the smallest individual capacitor in the string. The calculation returns that effective capacitance from Capacitance 1, Capacitance 2, and an optional Capacitance 3 (optional).

The result is used when a circuit requires multiple capacitors in series but must be analyzed as one effective capacitance. Typical applications include capacitor voltage-sharing arrangements, AC coupling networks, timing circuits, filtering, resonant circuits, and troubleshooting an existing capacitor string. The calculated value is the capacitance seen across the two outside terminals of the complete series connection.

Series Equivalent Capacitance

Capacitors in series do not add directly. Each capacitor stores the same series charge, while the applied voltage divides across the individual capacitors. The total capacitance therefore decreases as capacitors are added in series.

For two capacitors:

\(\displaystyle \frac{1}{C_\text{eq}} = \frac{1}{C_1} + \frac{1}{C_2}\)

For three capacitors:

\(\displaystyle \frac{1}{C_\text{eq}} = \frac{1}{C_1} + \frac{1}{C_2} + \frac{1}{C_3}\)

Where:

• \(C_\text{eq}\) = equivalent capacitance
• \(C_1\) = Capacitance 1
• \(C_2\) = Capacitance 2
• \(C_3\) = Capacitance 3 (optional)

The calculator applies the reciprocal relationship and returns Equivalent capacitance in microfarads (µF).

Required Capacitance Values

Enter the individual capacitor values as positive capacitance values.

Calculator field	Electrical meaning	Entry requirement
Capacitance 1	First capacitor connected in series	Required positive value
Capacitance 2	Second capacitor connected in series	Required positive value
Capacitance 3 (optional)	Third capacitor connected in series	Enter 0 to omit it
Equivalent capacitance	Effective capacitance across the full series string	Calculated result

All entered values must use the same unit basis. With the displayed µF fields, enter each value in µF and interpret Equivalent capacitance in µF. Do not mix µF, nF, and pF values without converting them first.

Calculation Example

Enter the following values:

Field	Value
Capacitance 1	10 µF
Capacitance 2	10 µF
Capacitance 3 (optional)	0 µF

Because the third value is 0, the calculation uses two capacitors:

\(\displaystyle \frac{1}{C_\text{eq}} = \frac{1}{10} + \frac{1}{10}\)

\(\displaystyle \frac{1}{C_\text{eq}} = 0.2\)

\(\displaystyle C_\text{eq} = 5\ \mu F\)

Equivalent capacitance: 5 µF

Two equal capacitors in series always produce one-half of either capacitor’s individual capacitance. A pair of 10 µF capacitors therefore behaves as a 5 µF equivalent capacitor.

Voltage Distribution in a Series String

Equivalent capacitance does not establish whether the capacitor string is suitable for an applied voltage. In a simple ideal series circuit, the voltage across each capacitor is inversely related to its capacitance: the smaller capacitance carries the greater share of the voltage.

For equal-value capacitors, the voltage divides equally in the ideal calculation. Two equal 10 µF capacitors across a 100 V source would each have an ideal 50 V share. Real capacitor leakage current, capacitance tolerance, dielectric characteristics, temperature, age, and frequency can shift that distribution.

When capacitors are connected in series to increase working-voltage capability, verify each component’s voltage rating and the manufacturer’s requirements for balancing or equalizing components. The calculated Equivalent capacitance addresses capacitance only; it does not determine voltage sharing, surge capability, ripple-current capability, polarity suitability, or failure behavior.

Field and Design Limits

Use the calculated value for circuit analysis after confirming the actual series connection and component characteristics.

• A capacitor string must be electrically in series: each internal junction connects only the adjacent capacitors, with the equivalent capacitance measured across the two end terminals.
• Enter 0 in Capacitance 3 (optional) only when no third capacitor is included. A physical capacitor cannot have zero capacitance in a working series string.
• Measured capacitance can differ from marked capacitance because of tolerance, temperature, frequency, DC bias effects, aging, or test-method conditions.
• Polarized capacitors require correct polarity and appropriate circuit conditions; series connection does not remove those requirements.
• This calculation does not replace component datasheet review or equipment-specific design requirements for voltage rating, leakage, ESR, ripple current, transient exposure, or safety approvals.

For circuit calculations requiring a specific capacitance value, use the Equivalent capacitance result together with the actual capacitor ratings and the operating conditions of the equipment.

Related workflows: Capacitor Parallel Value Calculator and Capacitor Code Calculator.