A capacitor stores electrical energy by holding equal and opposite charges on two conductive plates separated by an insulator. This calculator covers the three relationships every electronics project eventually needs: how charge, voltage, and capacitance relate; how much energy a charged capacitor holds; and how capacitance changes when multiple capacitors are wired together.
How the Capacitor Calculator works
The defining relationship for any capacitor is Q = C·V — the charge it holds is proportional to both its capacitance and the voltage across it. Rearranging this single equation lets you solve for whichever quantity you don't already know, which is exactly what the Charge & Voltage tab does.
The energy stored in a charged capacitor is E = ½CV², derived from integrating the work done moving charge onto the plates as voltage builds up. Because energy scales with the square of voltage, doubling a capacitor's voltage rating quadruples the energy it can store at that voltage — an important consideration when choosing capacitors for energy-storage applications like camera flashes or power-supply filtering.
Inputs and what they mean
Capacitance is entered in microfarads (µF), the unit printed on the overwhelming majority of real-world capacitors — everything from small ceramic disc capacitors (picofarads to nanofarads) to large electrolytic capacitors (hundreds to thousands of microfarads). Voltage is entered in volts and should reflect the actual voltage across the capacitor, not necessarily its maximum voltage rating. Charge is entered in microcoulombs, a unit you'll rarely see on a datasheet directly but that falls out naturally from Q = C·V once capacitance and voltage are known.
On the Series/Parallel tab, add as many capacitor values as your circuit needs — the calculator recomputes the combined value live as you edit or remove rows.
Limits and edge cases
This calculator models an ideal capacitor: it assumes no leakage current, no equivalent series resistance, and a fixed capacitance independent of voltage or frequency. Real capacitors — especially ceramic types — can lose a meaningful fraction of their rated capacitance at higher voltages or temperatures, so treat the results as a first-pass estimate rather than a substitute for a datasheet lookup. The calculator also does not check a capacitor's voltage rating; entering a voltage above what a real component can handle will still return a mathematically correct answer, but that component would fail in practice.