An improved formulation relating the contact angle to the surface coverage is presented and verified. The Ohmi et al. data (Particle Sci. Technol. 7, 229, 1993) for ultracleaning of wafer surfaces are analyzed and correlated mathematically. It is shown that the new formulation represents the Ohmi et al. and Englander et al. (J. Colloid Interface Sci. 179, 635, 1996) data satisfactorily. In addition, the present study provides some insight into the mechanism of the variation of the surface coverage and the contact angle.