Capacitor Calculator

This capacitor calculator is an all-in-one tool for working out the key values of a capacitor: capacitance, voltage, charge, stored energy, capacitive reactance, and the total of capacitors wired in series or parallel. Whether you are designing a power-supply filter, sizing a coupling capacitor, or checking a circuit by hand, it returns instant results with the formula spelled out.

It covers three calculation modes. Basic finds capacitance (C), voltage (V), charge (Q), and stored energy (E) from any two known values. Impedance gives the capacitive reactance (Xc) at a chosen frequency, plus optional AC current. Series & Parallel combines several capacitors into one equivalent capacitance. Every input accepts SI unit prefixes, so you can type the values printed on your components directly.

Private by design: every calculation runs in your browser. Nothing you enter is uploaded to a server or stored anywhere.

How to Use the Capacitor Calculator

Pick a calculation mode

Choose the Basic, Impedance, or Series & Parallel tab depending on what you need to solve.

Enter your known values

In Basic, fill in any two of capacitance, voltage, and charge. In Impedance, enter capacitance and frequency (voltage is optional). In Series & Parallel, type each capacitor value.

Set the right units

Use the dropdown beside each field to match your component (pF, nF, µF, mF, F for capacitance; mV, V, kV for voltage; Hz, kHz, MHz for frequency). Results auto-scale to the most readable prefix.

Read the results

Results update in real time as you type, with the formula and step-by-step substitution shown below each answer. The Impedance tab also draws a log-log chart of reactance against frequency.

In Basic mode the calculator tracks your last two inputs; entering a third value clears the oldest. Use Precision to set 2–6 decimal places, Examples to load common circuit values, and Reset to clear the current tab.

Features

Three Calculation Modes

Switch between Basic (C, V, Q, E), Impedance (Xc, AC current), and Series & Parallel combination with a single click.

Charge & Energy from Two Values

Enter any two of capacitance, voltage, and charge to find the third, with stored energy (E = ½CV²) calculated automatically.

Smart Input Tracking

In Basic mode the calculator remembers your last two entries; type a third value and the oldest field clears itself — no manual erasing.

Reactance & AC Current

Compute capacitive reactance (Xc) at any frequency, and add a voltage to also get the AC current through the capacitor.

Frequency Response Chart

The Impedance tab plots a log-log chart of reactance across the frequency spectrum, with a marker at your selected frequency.

Series & Parallel Combination

Add up to 10 capacitors, each with its own unit, and see the total equivalent capacitance for series and parallel layouts.

Full SI Prefix Support

Pick picofarads to farads, millivolts to kilovolts, and hertz to megahertz; results auto-scale to the clearest prefix.

Formula Display

Every result shows the formula used and the step-by-step substitution, so you can verify the math and learn the relationships.

Quick Examples

Load preset values for common circuits — power-supply filters, audio filters, RF coupling, and more — to get started fast.

Adjustable Precision

Set the number of decimal places from 2 to 6 to match the accuracy you need for the job.

Frequently Asked Questions

How do you calculate capacitors in series?

Series capacitance is found by adding the reciprocals: 1/C_total = 1/C1 + 1/C2 + …. The total is always smaller than the smallest capacitor in the chain. Open the Series & Parallel tab, choose Series, and enter your values to see the equivalent capacitance instantly.

How do you calculate capacitors in parallel?

Parallel capacitors simply add together: C_total = C1 + C2 + …, giving a larger total than any single component. Pick the Series & Parallel tab, switch to Parallel, and type each value — the running total updates as you go.

Do capacitors in series add or divide?

Series capacitors do not add — they combine like resistors in parallel, so the total capacitance drops. Two equal capacitors in series give half the value of one. The upside is voltage rating: because the voltage is shared across them, a series stack can handle more voltage than a single capacitor.

What is the relationship between Q, C, and V?

Charge equals capacitance times voltage: Q = C × V. Know any two of the three and the calculator finds the missing one. Capacitance (C) measures the ability to store charge and is given in farads (F), from picofarads in RF work to thousands of microfarads in power supplies.

How much energy does a capacitor store?

The stored energy is E = ½ × C × V², which can also be written as E = ½QV or E = Q²/(2C). In Basic mode the calculator shows the energy alongside every result, so you can size capacitors for flash circuits, buffers, or hold-up time without a separate step.

What is capacitive reactance (Xc)?

Capacitive reactance is the opposition a capacitor presents to alternating current. It depends on both capacitance and frequency: Xc = 1 / (2πfC). Higher frequency or larger capacitance means lower reactance. The Impedance tab calculates Xc and plots how it changes across frequency.

What units does the capacitor calculator support?

Capacitance: pF, nF, µF, mF, F. Voltage: mV, V, kV. Charge: pC, nC, µC, mC, C. Frequency: Hz, kHz, MHz. You can mix units freely between fields, and every result is auto-scaled to the most readable prefix.