On the wiki page for Dirac Sea, it's pointed out that the Sea of Dirac created by the twelfth angel Leliel is described as having a diameter of 680 meters and a thickness of 3 nanometers. Assuming, as is done in the article, that that means it would appear to be circular when viewed from above, that makes it a (very short) cylinder. Its volume would therefore be approximately one cubic decimeter, not one cubic millimeter, as the article states.
A cubic decimeter is about a quart; still not nearly enough space for an Evangelion, but it is one million times the volume of a cubic millimeter.

EDIT: A more precise definition of a cubic decimeter would be a liter. Derp.