Capacitor Charge Calculator
From the capacitance and the voltage, get the charge a capacitor stores and the energy it holds — the two numbers behind every smoothing, flash, and filter circuit.
What is capacitor charge?
Capacitance and voltage in, charge and energy out
A capacitor stores electric charge on a pair of plates, and the amount it holds depends on two things: how big the capacitor is (its capacitance) and how hard you push (the voltage). The relationship is wonderfully simple — the stored charge equals the capacitance times the voltage, written Q = C × V. Once you know the capacitance and the voltage, the charge is fixed, and so is the energy the capacitor banks for later, E = ½ × C × V². That makes capacitance and voltage the two inputs you need for smoothing a power supply, sizing a flash capacitor, or designing a filter.
Enter the capacitance in farads and the voltage in volts to get the stored charge and energy instantly.
Two short formulas, both built from the capacitance (C) and the voltage (V).
charge = C × VThe charge is simply the capacitance times the voltage (C × V). The energy — how much work the capacitor can do when it discharges — is half the capacitance times the voltage squared (½ × C × V²). Because the voltage is squared in the energy formula, the energy grows much faster than the charge as the voltage rises.
Suppose a 1000 µF capacitor (0.001 F) is charged to 12 V.
Charge
0.001 × 12 = 0.012 C — the charge held on the plates.
Energy (squared voltage)
½ × 0.001 × 12² = ½ × 0.001 × 144 = 0.072 J — the energy stored.
Cross-check
Energy also equals ½ × Q × V = ½ × 0.012 × 12 = 0.072 J — the same answer two ways.
The two outputs answer two different practical questions. The charge (0.012 C for 0.001 F at 12 V) tells you how much electric charge sits on the plates — it is proportional to both the capacitance and the voltage, so doubling either one doubles the charge. The energy (0.072 J) tells you how much work the capacitor can deliver when it discharges, which matters whenever you need a burst of power, such as a camera flash or a hold-up capacitor that keeps a circuit alive through a brief power dip. The key insight is that charge rises in step with voltage, but energy rises with the square of it: at a fixed capacitance, doubling the voltage from 12 V to 24 V doubles the charge but quadruples the energy. Notice too that capacitance is usually tiny — microfarads, nanofarads, even picofarads — so real-world charges come out small, often a fraction of a coulomb. Reach for the energy figure whenever the capacitor has to do work, and the charge figure whenever you care about how much it holds.
The formulas are exact for an ideal capacitor, but a couple of practical points are worth keeping in mind.
Ideal capacitors and SI units
Q = C × V and E = ½ × C × V² describe an ideal capacitor at a steady voltage. Real parts have leakage, a tolerance on their printed value, and a maximum rated voltage you must not exceed — going over it can destroy the capacitor. Remember that data sheets quote capacitance in microfarads (µF), nanofarads (nF), or picofarads (pF), so convert to farads first: 1000 µF = 0.001 F. This tool solves only the charge and energy from the capacitance and voltage; to find the capacitance or voltage instead, rearrange the formula (capacitance = Q ÷ V, voltage = Q ÷ C).