Capacitor Energy Calculator
Find energy stored in a capacitor.
Capacitance in farads (1 µF = 0.000001 F).
Results update as you type.
How it works
A capacitor stores energy in the electric field between its plates, and this capacitor energy calculator finds how much, in joules, from the capacitance and the voltage across it. The larger the capacitance and the higher the voltage, the more energy is held, with voltage counting twice over because it appears squared. That stored energy can be released quickly to deliver a burst of power when the circuit demands it. This matters in many applications: camera flashes, defibrillators, power-supply smoothing, motor-start circuits, and energy-recovery systems all rely on capacitors to store and dump energy on cue. Knowing the stored energy tells you how big a flash or pulse you can deliver, how much ride-through a supply has during a dropout, and how dangerous a charged capacitor bank is to handle, since large ones store enough energy to injure. The formula works because the voltage on a capacitor rises in step with the charge you add, so the work to charge it fully is the triangular area under the charge-voltage line, giving one-half capacitance times voltage squared. Because voltage is squared, doubling it quadruples the stored energy. Electronics engineers, students, and technicians use a capacitor energy calculator to size storage and assess safety.
E = ½ × C × V²
The energy stored in a capacitor equals one-half of its capacitance times the voltage squared. Voltage is squared because as charge accumulates on the plates, the voltage rises in proportion, and the work done to add each new bit of charge grows with the voltage already present. The stored energy is the area under the charge-versus-voltage line, which is a triangle, giving the one-half factor.
Source:Standard electrical engineering (E = ½CV²)
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
Stored energy updates instantly as you type — no button to press.
Frequently asked questions
How much energy does a capacitor store?
A capacitor stores energy equal to one-half its capacitance multiplied by the square of the voltage across it, measured in joules. A one-millifarad capacitor at twelve volts stores half times 0.001 times 144, or 0.072 joules. Larger capacitance and higher voltage both increase the stored energy, but because voltage is squared it has the stronger effect on the total energy held.
Why is voltage squared in the formula?
As a capacitor charges, its voltage rises in proportion to the charge stored. The work needed to push each additional bit of charge onto the plates grows with the voltage already there, so the total energy is the triangular area under the charge-versus-voltage graph. That triangle gives one-half capacitance times voltage squared, which is why doubling the voltage quadruples the energy held.
What units should I enter?
Enter capacitance in farads and voltage in volts to get energy in joules. Most real capacitors are rated in microfarads, nanofarads, or picofarads, so convert first: one microfarad is 0.000001 farad, one nanofarad is 0.000000001 farad. Entering a microfarad value directly without converting would overstate the energy by a factor of a million, so always convert to farads first.
Are charged capacitors dangerous?
They can be. Large capacitors charged to high voltage, such as those in power supplies, camera flashes, or defibrillators, store enough energy to deliver a painful or even lethal shock long after power is removed. Always discharge big capacitors safely through a resistor before handling a circuit. This calculator's energy figure helps you judge the hazard: more stored joules means a more dangerous discharge.
How is stored energy different from charge?
Charge is the amount of separated electric charge on the plates, equal to capacitance times voltage, measured in coulombs. Energy is the work stored in the resulting electric field, equal to one-half capacitance times voltage squared, measured in joules. Charge rises linearly with voltage while energy rises with voltage squared, so they are related but distinct quantities describing different aspects of the charged capacitor.