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Parallel-Plate Capacitor Calculator

Calculate a parallel-plate capacitor's capacitance, stored charge and energy, and the electric field between the plates, from plate area, separation, and dielectric.

Capacitance
88.542 pF
Charge stored
0.4427 nC
Energy stored
1.1068 nJ
Electric field between plates
5,000 V/m

How it works

This site's existing Capacitor Energy Storage calculator takes a capacitor's capacitance and voltage as given — it has no way to say what a capacitor you're designing from scratch would actually be rated at. This calculator fills that gap with the standard parallel-plate formula C = ε₀·εᵣ·A ÷ d (ignoring fringing fields at the plate edges, the same idealization every introductory derivation makes), where ε₀ is the vacuum permittivity, a fixed physical constant, and εᵣ is the dielectric's relative permittivity — a material property you supply directly (1 for vacuum/air, higher for an actual insulator) rather than this calculator guessing a material from a list.

Once capacitance is known, charge Q = C·V and energy E = ½·C·V² follow the same identities the Capacitor Energy Storage calculator already uses. The electric field between the plates, E = V ÷ d, is reported alongside them since it's the practical figure that determines whether a dielectric will suffer electrical breakdown at a given voltage — a thinner gap or higher voltage both raise this field even if the capacitance itself stays the same.

FAQ

Why does a smaller plate separation increase capacitance?

Capacitance measures how much charge builds up per volt of potential difference, and moving the plates closer together strengthens the electric field each unit of charge produces between them — so less voltage is needed to hold the same charge, which is exactly what a higher capacitance means. This is also why electric field (E = V/d) rises as the plates get closer even when the capacitance is going up, not down — it's driven by distance directly, not by the amount of charge stored.

What does the relative permittivity actually represent?

It's a measure of how much a dielectric material between the plates reduces the effective electric field compared to vacuum, for the same charge — a property of the insulating material (air, glass, ceramic, etc.) that you look up or measure for whatever material you're using, not something this calculator can know on its own. A higher εᵣ means more capacitance from the same geometry, which is exactly why real capacitors use a dielectric instead of an air gap.

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