Prior research has purported to show that words with infrequent phoneme-grapheme correspondences are more difficult to spell than words with frequent phoneme-grapheme correspondences. Defining exactly what a phoneme-grapheme relationship is, however, is not necessarily straightforward. There are a number of different assumptions that can be made. In this study, we developed four metrics of sound-spelling contingency based on all monosyllabic English words, including those with complex morphology. These metrics differed in the extent to which they included assumptions about spelling. The psychological reality of these different metrics was evaluated against data from a large-scale study of skilled adult spelling and a nonword spelling experiment. The results suggest that when spelling, people are sensitive to positional information, morphological status, vowel type, and a number of more idiosyncratic constraints.