engineering

Capacitor Calculator

Calculate the energy stored in a capacitor or its capacitive reactance at any frequency.

Capacitance (µF)

Voltage (V)

Stored energy

0.072 J

Energy stored in the capacitor’s electric field: E = ½CV²

In millijoules

72 mJ

In microjoules

72,000 µJ

How it works

1Choose a mode — stored energy or reactance.
2Enter the capacitance in microfarads (µF) plus the voltage or frequency for that mode.
3The calculator applies the relevant formula and shows the result with unit conversions.

Sizing a backup capacitor bank and checking it stores enough energy.
Designing an AC filter and checking a capacitor’s reactance at a target frequency.
Evaluating discharge energy in a camera flash or similar capacitor.

What formula does the energy mode use?

E = ½ × C × V². A 1000 µF capacitor at 12 V stores ½ × 0.001 × 144 = 0.072 J (72 mJ).

Why does reactance fall as frequency rises?

Xc = 1 ÷ (2πfC); frequency is in the denominator, so higher frequency means lower reactance — a capacitor passes high-frequency AC and blocks DC.

Why does it show — at zero frequency or capacitance?

The reactance denominator 2πfC becomes zero, making reactance infinite (undefined), so the calculator shows — for that input.

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