Capacitance & Capacitor Energy Calculator
Capacitance, charge, voltage and stored energy — plus the parallel-plate geometry formula.
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Parallel-plate geometry (optional)
Formulas
Q = C · V
E = ½ · C · V² = Q²/(2C) = ½ · Q · V
Parallel plate: C = ε₀ · εr · A / d (ε₀ = 8.854×10⁻¹² F/m)
E = ½ · C · V² = Q²/(2C) = ½ · Q · V
Parallel plate: C = ε₀ · εr · A / d (ε₀ = 8.854×10⁻¹² F/m)
Physics behind capacitors
A capacitor stores electrical energy in the electric field between two conductors separated by an insulator (dielectric). Its capacitance is a purely geometric and material property — bigger plates and thinner gaps give more capacitance; inserting a dielectric with εr > 1 increases it further. Charge and voltage are proportional (Q = C·V), and the energy scales with voltage squared.
Worked example
C = 100 μF, V = 12 V
Q = C·V = 100×10⁻⁶ × 12 = 1.2×10⁻³ C = 1.2 mC E = ½·C·V² = ½·100×10⁻⁶·144 = 7.2×10⁻³ J = 7.2 mJ
Related tools
FAQs
What is capacitance?
Ratio of stored charge to voltage, in farads.
How much energy does a capacitor store?
E = ½·C·V².