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The hypothesis that an unmagnetized plasma will form a meniscus sheath above an ion extraction aperture on the electric field magnitude contour, |E|=Ep=Te/λD, is tested. The hypothesis is assumed to be true, that the ion extraction surface of a single aperture ion extraction optic is given by the vacuum Laplace electric field magnitude contour equal to Ep. The ion current extracted from this surface for a single aperture is calculated analytically. The analytically calculated current is compared to a particle-in-cell simulation of ion extraction from a single aperture, for densities ranging from 1.49·1014 to 1.49·1020 m-3 and electron temperatures of 1.35-2.7 eV. The simulated extraction current and extraction area agree with the calculated current and area very well, with deviations of only 0.1%-8% relative to the simulated value.