Analytic expressions derived from a simplified model are invaluable because they often provide deep insight into geophysical phenomena. Such is the case with potential and gravity changes. Here we present expressions of potential and gravity changes caused by faulting on a finite rectangular plane buried in a homogeneous half-space. The expressions can be used to evaluate coseismic changes in surface gravity and geoid height. Observed gravimetric data combined with our formulae thus provide constraints on the fault geometry and magnitudes of dislocation.