Capacitor Calculator

Free Capacitor Calculator

This Capacitor Calculator finds charge, stored energy, or capacitance from the values you know. Choose Q = C x V to calculate charge, E = one-half C V squared for stored energy, or C = Q / V for capacitance. It automatically converts microfarads and microcoulombs into SI base units and shows every calculation step.

The labelled plate diagram makes capacitor behaviour easy to see. A voltage difference causes positive and negative charge to collect on opposite conducting plates, with energy stored in the electric field between them. It is useful for students, hobby circuits, and basic electronics design.

What Is a Capacitor?

A capacitor is an electronic component that stores electric charge and energy in an electric field. It typically contains two conductive plates separated by an insulating material called a dielectric. When voltage is applied, equal and opposite charges build up on the plates.

Capacitors are used for smoothing power supplies, timing circuits, filters, motor starting, signal coupling, and short bursts of energy. Unlike a battery, a capacitor usually stores less total energy but can charge and discharge very quickly.

Capacitor Formula: Charge

The basic capacitor equation connects charge, capacitance, and voltage:

• Q = C x V
• Q is charge in coulombs, C is capacitance in farads, and V is voltage in volts.
• 1 farad is a very large practical unit; microfarads (microF), nanofarads (nF), and picofarads (pF) are common.
• Example: 100 microF at 12 V stores 1,200 microC.

Energy Stored in a Capacitor

The energy formula for a charged capacitor is E = one-half x C x V squared. Energy is measured in joules. Voltage has a squared effect, so doubling voltage increases stored energy by four times when capacitance is unchanged.

For a 1,000 microF capacitor at 12 V, energy is 0.5 x 0.001 x 12 squared = 0.072 J. Even when the energy seems small, large capacitors and high voltages can deliver harmful current, so handle charged capacitors carefully.

How to Calculate Capacitance

To find capacitance from charge and voltage, rearrange Q = C x V into C = Q / V. Convert charge to coulombs before dividing by volts. A capacitor holding 1,200 microC at 12 V has C = 0.0012 / 12 = 0.0001 F, which equals 100 microF.

Always keep unit prefixes visible. One microfarad is 0.000001 F and one microcoulomb is 0.000001 C. Missing this conversion changes the answer by a factor of one million.

Capacitor Units and Ratings

Capacitance is measured in farads. Common units are microfarads, nanofarads, and picofarads. One microfarad equals 1,000 nanofarads and one nanofarad equals 1,000 picofarads. Capacitors also have a maximum voltage rating that must exceed the circuit voltage with suitable margin.

Capacitance tolerance, temperature, DC bias, leakage current, equivalent series resistance, and polarity can affect real behaviour. Electrolytic capacitors are commonly polarized and must be installed with correct polarity; reversing them can cause failure or danger.

Capacitors in Series and Parallel

Capacitors behave opposite to resistors when combined. Capacitors in parallel add directly: C total = C1 + C2 + C3. Capacitors in series use reciprocal addition: 1/C total = 1/C1 + 1/C2. Series capacitance is lower than the smallest capacitor, while parallel capacitance is larger than the largest individual capacitor.

Series connections can increase voltage capability when voltage sharing is managed, while parallel connections increase total capacitance. Use components with appropriate ratings and consider balancing resistors in high-voltage series capacitor banks.

Charging, Discharging, and RC Circuits

A resistor-capacitor, or RC, circuit charges and discharges gradually rather than instantly. The time constant is tau = R x C. After one time constant a charging capacitor reaches about 63% of its final voltage; after five time constants it is very close to fully charged.

RC circuits are used for delays, filters, oscillators, debouncing switches, and pulse shaping. Use the RC Circuit Calculator for timing calculations involving resistance and capacitance.

Capacitor Safety

Disconnect power and safely discharge capacitors before touching a circuit. Large electrolytic capacitors, camera flash capacitors, power supplies, and high-voltage equipment can retain dangerous charge after power is removed. Use an appropriate discharge method and follow the manufacturer's recommendations.

Never exceed voltage, ripple-current, temperature, or polarity ratings. This calculator is for education and preliminary calculations; it does not replace a complete circuit safety review.

Capacitor Calculator FAQs

Use Q = C x V to calculate charge, E = one-half C V squared for stored energy, and C = Q / V for capacitance. Capacitance is measured in farads, but microfarads are common. A capacitor stores charge on plates and energy in an electric field, and its voltage rating must not be exceeded.