Prior probabilities of graphemes and conditional probabilities for their pronunciation as specific phonemes are given based on a corpus of 17,310 English words. Phonemes are as given in recent editions ofWebster's New Collegiate Dictionary, with minor revisions; graphemes are defined as letters or letter clusters corresponding to single phonemes. Grapheme-phoneme probabilities were derived from a revised table of frequency of occurrence of phoneme-to-grapheme correspondences generated in a study of spelling regularities (P. R. Hanna, J. S. Hanna, Hodges, {\&} Rudorf, 1966). This quantitative descriptive information provides an index of the strength of particular grapheme-phoneme associations in English. Suggestions are made for the utilization of these probabilities as estimates of spelling/sound predictability in reading research.