The AC potential drop technique is widely used in non-destructive testing for sizing surface-breaking cracks in metals but, in order to find the through-thickness penetration of a crack, its inclination to the surface is needed as well as its size. By modelling the electric field around an inclined crack in the extremes of both large and small skin depth, it is shown in this paper that the asymmetry in the voltage signal across the crack can be used to find the angle of inclination. Experimental results obtained from a range of metals confirm the theoretical findings.