Generated on: June 17, 2026 at 05:24 PM

Capacitor Charge & Energy Calculator

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Solve forCharge Q
Capacitance100 µF
Voltage12 V
Charge1.2 mC

Generated with OneCalc · https://onecalc.app/en/physics/capacitor-energy-charge

Physics

Capacitor Charge & Energy Calculator

Find the charge, voltage, capacitance and stored energy of a capacitor from Q = C·V and E = ½·C·V². Choose what to solve for, enter the two known values, and read the result plus the energy stored in the electric field.

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Capacitor charge and energy

A capacitor stores electric charge on two conducting plates separated by an insulator. The amount of charge it holds is set by its capacitance and the voltage applied across it: Q=C⋅VQ = C \cdot V. The charge QQ is measured in coulombs, the capacitance CC in farads, and the voltage VV in volts. Rearranging the same relationship lets you find any one of the three quantities from the other two.

This calculator solves for charge, voltage or capacitance and always reports the energy stored in the capacitor's electric field.

Charge, voltage and capacitance

The defining equation Q=C⋅VQ = C \cdot V says that, for a fixed capacitor, the stored charge is directly proportional to the applied voltage — double the voltage and you double the charge. Capacitance is the constant of proportionality: a larger capacitance holds more charge at the same voltage. Solving the equation the other way gives V=Q/CV = Q/C and C=Q/VC = Q/V.

QuantitySymbolMeaning
ChargeQQCharge stored on the plates, in coulombs
CapacitanceCCCapacitance of the capacitor, in farads
VoltageVVPotential difference across the plates
EnergyEEEnergy stored in the electric field

Stored energy

Charging a capacitor takes work, because each added increment of charge must be pushed against the voltage already present. Adding up that work gives the energy stored in the field:

E=12CV2=12QV=Q22CE = \tfrac{1}{2} C V^2 = \tfrac{1}{2} Q V = \frac{Q^2}{2C}

The three forms are equivalent — which one is most convenient depends on the quantities you know. The key feature is the V2V^2 dependence: the energy grows with the square of the voltage, so doubling the voltage stores four times the energy.

Worked example

A 100 μF100\ \mu\text{F} capacitor is charged to 12 V12\ \text{V}. Its stored charge and energy are:

Q=C⋅V=100×10−6×12=1.2×10−3 C=1.2 mC\begin{aligned} Q &= C \cdot V \\ &= 100 \times 10^{-6} \times 12 \\ &= 1.2 \times 10^{-3}\ \text{C} = 1.2\ \text{mC} \end{aligned} E=12CV2=12×100×10−6×122=7.2×10−3 J=7.2 mJ\begin{aligned} E &= \tfrac{1}{2} C V^2 \\ &= \tfrac{1}{2} \times 100 \times 10^{-6} \times 12^2 \\ &= 7.2 \times 10^{-3}\ \text{J} = 7.2\ \text{mJ} \end{aligned}

Entering a capacitance of 100 µF and a voltage of 12 V reproduces both results.

Why capacitances are so small

One farad is a very large capacitance, so real components are usually a small fraction of it. Picofarad (10−12 F10^{-12}\ \text{F}) and nanofarad (10−9 F10^{-9}\ \text{F}) capacitors appear in radio and signal circuits, microfarad (10−6 F10^{-6}\ \text{F}) capacitors in general electronics and power smoothing, and only specialised supercapacitors reach whole farads. This calculator accepts pF, nF, µF, mF and F so you can work in whatever scale your circuit uses.

Limitations

The relationships above assume an ideal capacitor with a single, well-defined capacitance and no leakage. Real capacitors have a small series resistance, a maximum rated voltage that must not be exceeded, and a capacitance that can drift with temperature, frequency and applied voltage. For precise work, consult the component's datasheet rather than the nominal printed value.

Frequently Asked Questions (FAQ)

What is the formula for capacitor charge?

The charge stored on a capacitor is Q = C·V, where C is the capacitance in farads and V is the voltage across it. Charge is measured in coulombs: a 100 µF capacitor at 12 V holds Q = 100×10⁻⁶ × 12 = 1.2×10⁻³ C = 1.2 mC. Rearranged, the formula also gives voltage (V = Q/C) or capacitance (C = Q/V).

How much energy does a capacitor store?

A charged capacitor stores energy in its electric field: E = ½·C·V², which can also be written E = ½·Q·V or E = Q²/(2C). For a 100 µF capacitor at 12 V, E = ½ × 100×10⁻⁶ × 12² = 7.2×10⁻³ J = 7.2 mJ. Because energy grows with the square of the voltage, doubling the voltage quadruples the stored energy.

Why are capacitors rated in microfarads or picofarads?

One farad is an enormous amount of capacitance, so practical capacitors are usually a tiny fraction of it. Common values run from a few picofarads (1 pF = 10⁻¹² F) in radio-frequency circuits, through nanofarads and microfarads (1 µF = 10⁻⁶ F) in general electronics, up to thousands of microfarads in power-supply smoothing. Supercapacitors are the exception, reaching whole farads.

How is a capacitor different from a battery?

Both store energy, but a capacitor stores it physically in an electric field rather than chemically. That lets a capacitor charge and discharge in a small fraction of a second and survive far more cycles, but it holds much less energy than a battery of the same size and its voltage drops steadily as it discharges. Capacitors are used for fast bursts, filtering and smoothing; batteries for sustained energy supply.

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