White pigments impart opacity to films and coatings by virtue of their ability to scatter incident light. This study considers a homogeneous coating that contains a low concentration of randomly dispersed, monodisperse pigment particles. The optical properties are determined using a lattice model with cell size defined by the diameter (d) of the particles. For pure scattering, the contrast ratio (CR) is an algebraic function of the scattering coefficient (K), pigment volume fraction ( p), and coating layer thickness (L), as follows: CR = [1 + d/L (1-kappaphi/kappaphi)](-1) When tested against literature data for white films opacified with titanium dioxide, an empirical expression with a single adjustable constant provides a better interpolation formula than the above equation. This discrepancy is attributed to the contribution of a minor amount of absorption to the measured opacity.