  We calculate the effects of spot size on pulse profiles of moderately
rotating neutron stars. Specifically, we quantify the bias introduced in radius
measurements from the common assumption that spots are infinitesimally small.
We find that this assumption is reasonable for spots smaller than
10$^\circ$-18$^\circ$ and leads to errors that are $\le$10% in the radius
measurement, depending on the location of the spot and the inclination of the
observer. We consider the implications of our results for neutron star radius
measurements with the upcoming and planned X-ray missions NICER and LOFT. We
calculate the expected spot size for different classes of sources and
investigate the circumstances under which the assumption of a small spot is
justified.
