Capacitor Charge Calculator — Q = C × V

Q = C × V. Stored charge in coulombs equals capacitance in farads times voltage in volts. This is the defining equation of capacitance — one farad stores one coulomb at one volt. All other formulas (E = ½CV², τ = RC, X꜀ = 1/(2πfC)) grow from this single relationship.

Number of electrons N = Q / e, where e = 1.602 × 10⁻¹⁹ C is the elementary charge. A 1 µF capacitor charged to 5V stores Q = 5 µC of charge — divide that by e and you get about 31.25 billion electrons. The electron count is huge even for very small capacitors because a single coulomb represents roughly 6.24 quintillion electrons.

No — current I is the time derivative of charge: I = dQ/dt. A capacitor has zero steady-state DC current because once it charges, Q stops changing. But during charge and discharge, a current flows that equals the rate at which Q is changing. This is why capacitors pass AC and block DC — AC continuously recharges and discharges the plates.

During charging through a resistor R, the peak displacement current is I₀ = V / R at the moment the switch closes. It decays exponentially with the same time constant τ = RC. The calculator above shows this peak current when you enter a resistance. For a 10 µF cap charged to 12V through a 1 kΩ resistor, I₀ = 12 mA.

In series, every capacitor in the string stores the same charge Q. This is exactly the same rule as current in a series circuit — charge is conserved, so the same Q flows through every capacitor. Voltage divides: V_total = V₁ + V₂ + V₃…, where V_i = Q / C_i. This is why you cannot just add voltages in a series bank.

In parallel, every capacitor shares the same voltage, and total charge adds: Q_total = Q₁ + Q₂ + Q₃… = V × (C₁ + C₂ + C₃…). This follows directly from Q = CV and C_total = C₁ + C₂ + C₃. Parallel banks store more total charge than any single capacitor in the bank.

The charge on one plate of a capacitor is always +Q, and on the other plate −Q. The total stored charge in the capacitor is zero — there are no net excess electrons on the device as a whole. What is stored is energy in the electric field between the plates, not an excess of charge on the device.

1 ampere-hour = 3 600 coulombs. Divide coulombs by 3 600 to get Ah, then multiply by 1 000 to get mAh. The conversion factor is the same regardless of voltage, because charge and energy have different units. A capacitor holding 2.5 coulombs has about 0.694 mAh of charge — regardless of whether those coulombs are at 1V or 100V.