Generative phonologists use contrastive minimal pairs to determine functional phonological units in a language. This technique has been extended for clinical purposes to derive phonemic inventories for children with phonological disorder, providing a qualitative analysis of a given child's phonological system that is useful for assessment, treatment, and progress monitoring. In this study, we examine the single-word productions of 275 children with phonological disorder from the Learnability Project (Gierut, 2015b) to confirm the relationship between phonemic inventory - a measure of phonological knowledge - and consonant accuracy - a quantitative, relational measure that directly compares a child's phonological productions to the target (i.e. adult-like) form. Further, we identify potential percentage accuracy cutoff scores that reliably classify sounds as in or out of a child's phonemic inventory in speech-sound probes of varying length. Our findings indicate that the phonemic function of up to 90% of English consonants can be identified from percentage accuracy for preschool-age children with phonological disorder when a sufficiently large and thorough speech sample is used.