We present a simple and practical data structure for storing a (not necessarily convex) polyhedron P which can, given a query surface S cutting the polyhedron, determine the volume and the area of the portion of the polyhedron above S. The queries are answered in a time linear in the size (complexity) of S. The space and preprocessing time for this data structure are linear in the size of P. We also present an intermediary data structure for planar graphs which is of independent interest.