Capacitance Calculator
Find capacitance and stored energy from charge and voltage.
Results update as you type.
How it works
Capacitance measures how much electric charge a capacitor can hold for each volt applied across its plates, and this capacitance calculator finds it by dividing the stored charge by the voltage. The result is given in farads, though real capacitors are usually rated in the far smaller microfarads, nanofarads, or picofarads. The calculator also reports the energy stored in the capacitor's electric field, which equals half the charge multiplied by the voltage. Capacitors are among the most common components in electronics, used to smooth power supplies, filter signals, tune radio circuits, store energy for camera flashes, and set timing in oscillators. Understanding the relationship between charge, voltage, and capacitance is fundamental to circuit design, because it determines how quickly a capacitor charges and discharges and how much energy it can deliver. Students of physics and electrical engineering meet this relationship early, and hobbyists building circuits use it to choose the right component for a job. Because energy grows with the square of the voltage, doubling the voltage on a fixed capacitor quadruples the stored energy, a fact that matters for both performance and safety. Enter the charge and the voltage to get both values instantly.
C = Q / V; E = ½·Q·V
Capacitance is the amount of electric charge a component stores per volt applied across it, so it equals the charge divided by the voltage and is measured in farads. The energy stored in the electric field is half the charge times the voltage, which also equals half the capacitance times the voltage squared. A larger capacitance holds more charge at the same voltage, and the stored energy rises with the square of the voltage.
Source:Electromagnetism (definition of capacitance)
We review all our tools from time to time to ensure accuracy.
Worked example
How to use this calculator
- 1
Enter your values
Enter charge (q) and voltage (v).
- 2
Adjust the options
Fine-tune any options to match your situation.
- 3
Read your result
Capacitance updates instantly as you type — no button to press.
Frequently asked questions
What is capacitance?
Capacitance is a measure of a component's ability to store electric charge for a given voltage, defined as the charge stored divided by the voltage across it. Its unit is the farad. A higher capacitance means the component holds more charge at the same voltage. Capacitance depends on the physical design of the capacitor, such as its plate area, spacing, and the insulating material between the plates.
What is a farad?
The farad is the SI unit of capacitance, equal to one coulomb of charge stored per volt applied. One farad is a very large amount of capacitance, so practical capacitors are usually rated in microfarads, nanofarads, or picofarads, which are millionths, billionths, and trillionths of a farad. The calculator returns the value in farads, which you can convert to these smaller units as needed.
How much energy does a capacitor store?
The energy stored in a capacitor equals half the charge multiplied by the voltage, which can also be written as half the capacitance times the voltage squared. Because the voltage term is squared, the stored energy rises steeply as voltage increases. This energy is held in the electric field between the plates and is released when the capacitor discharges through a circuit.
How does capacitance relate to charge and voltage?
Charge, voltage, and capacitance are linked by the equation charge equals capacitance times voltage. For a fixed capacitor, adding more charge raises the voltage proportionally, and applying more voltage forces more charge onto the plates. Capacitance itself is a constant set by the capacitor's construction, so it stays the same as charge and voltage change together in proportion.
Why does voltage matter for safety?
Because a capacitor's stored energy grows with the square of the voltage, high-voltage capacitors can hold dangerous amounts of energy even when small, and they can retain that charge long after a device is switched off. This is why large capacitors in power supplies and camera flashes must be discharged safely before handling. Always respect the voltage rating and discharge procedure for any capacitor.