A formula for the rms blur circle for Wolter telescopes has been derived using the transverse ray aberration expressions of Saha, Appl. Opt. 24, 1856-1863 (1985), Saha, Proc. Soc. Photo-Opt. Instrum. Eng. 444, 112-117 (1984), and Saha, Proc.Soc. Photo-Opt. Instrum. Eng. 640, 10-19 (1986). The resulting formula for the rmsblur circle radius over an image plane and a formula for the surface of best focus are based on third-, fifth-, andseventh-order aberration theory predict results in good agreement with exact ray tracing. It has also beenshown that one of the two terms in the empirical formula of VanSpeybroeck and Chase, Appl. Opt. 11, 440-445(1972), for the rms blur circle radius of a Wolter I telescope can be justified by the aberration theory results.Numerical results are given comparing the rms blur radius and the surface of best focus vs the half field anglecomputed by skew ray tracing and from analytical formulas for grazing incidence Wolter I-II telescopes and anormal incidence Cassegrain telescope. © 1990 Optical Society of America.