Enter your capacitance (with your chosen capacitance unit) and voltage (with your chosen voltage unit) into the Capacitor Energy Calculator to find the energy stored in your capacitor, plus the charge stored — shown in both standard and milliunit formats (mJ and mC).
Energy Stored
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Charge Stored
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Energy (mJ)
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Charge (mC)
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The energy stored in a capacitor is the electrical potential energy held in the electric field between its plates. This energy is calculated using the formula E = ½CV², where C is capacitance and V is voltage.
A capacitor stores energy by accumulating electric charge on its plates, which creates an electric field between them. The energy is stored in this electric field as potential energy that can be released when the capacitor discharges.
Use the formula E = ½CV², where E is energy in joules, C is capacitance in farads, and V is voltage in volts. You can also use E = ½QV or E = Q²/(2C) where Q is the charge in coulombs.
Using E = ½CV², with C = 120 pF (120 × 10⁻¹² F) and V = 1.5 V: E = ½ × (120 × 10⁻¹²) × (1.5)² = 135 × 10⁻¹² J = 135 picojoules.
The factor of ½ comes from the integration of power over time during charging. As voltage builds up linearly with charge, the average voltage during charging is V/2, resulting in the ½ factor in the energy formula.
Charge (Q) and energy are related through Q = CV. The energy can also be expressed as E = Q²/(2C) or E = ½QV, showing that energy increases quadratically with both charge and voltage.
Use farads for capacitance, volts for voltage, and coulombs for charge to get energy in joules. For practical calculations, microfarads (μF) and millivolts/volts are commonly used, with results in microjoules or millijoules.
Energy storage is directly proportional to capacitance. Doubling the capacitance doubles the stored energy at the same voltage. Higher capacitance values allow more energy storage for a given voltage rating.