b2KIT

Capacitor Calculator

Calculate capacitance in series and parallel, RC time constants, and energy storage.

Tested tool guide Tested browser tools Checked August 16, 2026

What Capacitor Calculator does, with a checked example

Capacitor Calculator answers three related circuit questions from entered component values. It combines capacitors connected entirely in series or parallel, calculates the time constant from resistance and capacitance, and finds ideal stored energy from capacitance and voltage. Values must be paired with the intended unit or prefix. A common surprise is that adding capacitors in series decreases equivalent capacitance, producing a result smaller than the smallest individual capacitor.

Worked example

A concrete input and expected output from the current implementation.

Input

Connection: Parallel
C1: 10 uF
C2: 20 uF

Expected output

Equivalent capacitance: 30 uF

Parallel capacitances add directly, so 10 uF + 20 uF = 30 uF.

How the result is produced

1

Combining capacitors

For a parallel connection, the calculator adds the capacitances: Ceq = C1 + C2 + .... For a series connection, it adds their reciprocals: 1 / Ceq = 1 / C1 + 1 / C2 + .... Capacitance values must first represent compatible units, such as converting nF and uF to a common scale.

2

RC and energy results

The RC section applies tau = R * C. Resistance in ohms multiplied by capacitance in farads produces a time constant in seconds. The energy calculation applies E = 1/2 * C * V^2, producing joules when capacitance is in farads and voltage is in volts. Doubling voltage therefore multiplies the calculated energy by four.

Good uses

  • Finding the replacement capacitance for two or more capacitors wired in one series or parallel group.
  • Estimating the characteristic timing of a resistor-capacitor delay, filter, or charging circuit.
  • Comparing the ideal energy stored by candidate capacitor values at a specified operating voltage.

Limits and checks

  • Check every metric prefix carefully. A microfarad is 1,000 nanofarads, so an incorrect unit selection can change the result by three orders of magnitude.
  • Series and parallel formulas require the stated topology. A mixed network must be reduced group by group, and an arbitrary circuit cannot be treated as one simple series or parallel set.
  • Results use ideal capacitance. Component tolerance, leakage, equivalent series resistance, temperature effects, voltage dependence, and dielectric losses can make physical behavior differ from the calculation.

Common questions

Why is the series result smaller than either capacitor?

In a series string, each capacitor contributes a reciprocal term to 1 / Ceq. Adding positive reciprocal terms makes 1 / Ceq larger than any individual reciprocal, so Ceq becomes smaller than the smallest capacitor. For two capacitors, the equivalent is C1 * C2 / (C1 + C2).

Does one RC time constant mean the capacitor is fully charged?

No. In an ideal first-order RC charging circuit, one time constant reaches about 63.2 percent of the final voltage. During discharge, about 36.8 percent remains after one time constant. The voltage approaches its final value asymptotically, so the calculated time constant is a characteristic interval, not a completion time.

References and verification

The example and behavioral notes were checked against the browser implementation. Standards and primary references below define the relevant format, formula, or platform behavior.

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