Capacitor Charge Calculator

This calculator works out the charge stored on a capacitor, the energy it holds, and the time constant of a resistor-capacitor circuit, from the capacitance, voltage and resistance. A capacitor stores electrical energy by holding charge on two plates separated by an insulator, and it is one of the most widely used components in electronics, found in power supplies, filters, timing circuits, camera flashes and countless other applications. Three quantities describe its behaviour. The charge it stores is simply the capacitance multiplied by the voltage across it, the fundamental relationship of capacitance. The energy stored is half the capacitance times the voltage squared, the energy released when the capacitor discharges. And when a capacitor charges or discharges through a resistor, it does so not instantly but over a characteristic time, the time constant, equal to the resistance times the capacitance, which sets the pace of timing and filter circuits. This tool computes all three. You enter the capacitance in farads, using scientific notation for the usual small values like microfarads, the voltage, and a resistance if you want the time constant, and the calculator returns the charge, the stored energy, and the time constant, along with the time to effectively fully charge, about five time constants. The results update as you type. Use it for electronics study, for designing timing and filter circuits, or for understanding energy storage. A capacitor reaches about 63 percent of the applied voltage after one time constant and is considered fully charged after five, a rule that governs the timing of many circuits. Because real capacitors are usually rated in microfarads, nanofarads or picofarads, the scientific notation input makes entering these small values straightforward.

Q = C x V. Energy = half x C x V squared. Time constant = R x C. A capacitor is ~63% charged after one time constant, effectively full after five.