Capacitor Charge Calculator
Find the charge and energy stored in a capacitor.
Results update as you type.
How it works
A capacitor stores electric charge and energy in an electric field, and this calculator finds both from the capacitance and voltage. You enter the capacitance in farads and the voltage across the capacitor, and it returns the charge stored in coulombs and the energy stored in joules. The charge is the capacitance times the voltage, a direct relationship meaning a larger capacitor or a higher voltage stores more charge. The energy, however, depends on the square of the voltage, being one half the capacitance times the voltage squared, so raising the voltage boosts stored energy far more than charge. Capacitors are fundamental components in electronics, used for smoothing power supplies, filtering signals, timing circuits, storing energy for camera flashes and defibrillators, and coupling stages of amplifiers. Real capacitances are usually small fractions of a farad, so values are often given in microfarads, nanofarads, or picofarads, which must be converted to farads before entering. Understanding stored charge and energy matters for designing circuits and for safety, since large charged capacitors can hold a dangerous amount of energy even after power is removed. This calculation is a staple of electronics education and practice. Enter the capacitance and voltage to compute the stored charge and energy.
Q = C·V; E = ½·C·V²
The charge stored on a capacitor equals its capacitance times the voltage across it. The energy stored equals one half of the capacitance times the voltage squared. Because energy depends on the square of the voltage, doubling the voltage quadruples the stored energy, while the charge only doubles.
Source:Electronics
We review all our tools from time to time to ensure accuracy.
Worked example
How to use this calculator
- 1
Enter your values
Enter capacitance and voltage.
- 2
Adjust the options
Fine-tune any options to match your situation.
- 3
Read your result
Charge stored updates instantly as you type — no button to press.
Frequently asked questions
How do you calculate capacitor charge?
Multiply the capacitance by the voltage across the capacitor. A 0.001-farad capacitor at 12 volts stores 0.012 coulombs of charge. The calculator does this and also computes the stored energy. Remember to convert microfarads or picofarads to farads before entering, since capacitances are usually small.
How much energy does a capacitor store?
The energy equals one half of the capacitance times the voltage squared. For a 0.001-farad capacitor at 12 volts, that is 0.072 joules. Because energy depends on voltage squared, doubling the voltage quadruples the energy, which is why high-voltage capacitors can store and release large bursts of energy.
What is capacitance measured in?
Capacitance is measured in farads, but a farad is a very large unit, so real capacitors are usually rated in microfarads, nanofarads, or picofarads. Convert these to farads before using the calculator: one microfarad is a millionth of a farad, one nanofarad a billionth, and one picofarad a trillionth.
Why does energy depend on voltage squared?
As a capacitor charges, the voltage rises with the accumulated charge, so each additional bit of charge is pushed against an increasing voltage. Integrating this work gives energy proportional to the voltage squared. The practical result is that stored energy climbs steeply with voltage, unlike charge, which rises only in direct proportion.
Are charged capacitors dangerous?
They can be. Large capacitors charged to high voltages store significant energy and can deliver a dangerous or lethal shock even after the power is disconnected, since they retain charge. Devices like camera flashes and power supplies use bleeder resistors to discharge them safely. Always treat large charged capacitors with caution.