The van der Pauw geometry has been widely used for the measurement of resistivities and Hall coefficients. Although the measurement of a Hall coefficient requires a finite magnetic field, it should be noted that van der Pauw’s expression is valid only in the limit of zero field; in addition to the Hall contribution, measurements in a finite magnetic field generally include a term associated with field-induced changes in the longitudinal resistivity. Although a simple solution to this problem entails taking the difference between readings in opposite field directions, there are circumstances where this may be impractical. In this note we present a straightforward extension of the van der Pauw calculation which allows a determination of the Hall coefficient from quantities measured in one field direction only.