Solve capacitance, plate area, plate separation, or dielectric constant for an ideal parallel-plate capacitor, with optional electric-field, stored-charge, and energy-density context from an applied voltage.
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Basic circuits
A parallel plate capacitance calculator keeps the geometry behind capacitance visible instead of hiding it behind a single number. This version solves capacitance, required plate area, plate separation, or dielectric constant for an ideal parallel-plate capacitor, and can add electric-field, stored-charge, and energy context when you enter an applied voltage.
This page can solve any one missing term in the ideal parallel-plate relation: capacitance, plate area, plate separation, or relative permittivity.
That makes it useful for first-pass capacitor sizing, dielectric comparisons, and back-solving the physical dimensions needed to reach a target capacitance.
Capacitance rises with plate area and dielectric constant, and falls as the gap between the plates increases. That is why thinner dielectrics, larger overlap area, and higher-permittivity materials all push the same plate pair toward a larger capacitance.
The solve-for modes help you move in either direction: from a known geometry to capacitance, or from a target capacitance back to the geometry or dielectric property you need.
C = εr × ε0 × A / d
The ideal parallel-plate model relates capacitance to plate area, separation, and relative permittivity.
A = C × d / (εr × ε0)
Rearranging the same relationship shows the plate area required for a target capacitance.
When voltage is provided, the calculator converts the solved geometry into electric field, stored charge, surface charge density, stored energy, and energy density. That keeps the result tied to an operating condition rather than only to a static physical layout.
Those supporting values are especially useful when you need to sanity-check whether a geometry looks plausible before moving on to dielectric strength, packaging, or measurement work.
Q = C × V; E = V / d
Stored charge and electric field follow directly from the solved capacitance, applied voltage, and separation.
U = 1/2 × C × V²
Stored energy translates the solved capacitance into an operating consequence at the stated voltage.
This calculator uses the ideal parallel-plate approximation. It does not model fringing fields, edge effects, dielectric losses, ESR, breakdown behaviour, temperature drift, or manufacturing tolerances.
Use it as a sizing and educational reference. If the design is sensitive to field shaping, high-voltage limits, or construction details, move to the analysis method that captures those effects explicitly.
Frequently asked questions
Because the same plate pair stores more charge per volt when the electric field spans a shorter distance. In the ideal formula, capacitance is inversely proportional to separation.
Relative permittivity describes how strongly the dielectric supports the electric field compared with vacuum. Higher εr increases capacitance for the same area and gap.
Only as a first-pass estimate. Real capacitors also depend on construction details, fringing, tolerances, losses, and breakdown limits that the ideal plate model does not include.
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