Sentence readability formulas have shown promise as an approach to assist both foreign language teaching and learning. Such formulae can theoretically enable the identification of sentences that are either too difficult or too easy for English learners of varying proficiency levels, but improvement over existing formulae is necessary. Therefore, we proposed and constructed a new sentence readability formula, and subsequently evaluated its validity. Results from leave-one-out (k-fold) cross-validation tests showed that sentence readability as measured by our formula strongly correlated (r = 0.88, p < 0.001) with the readability as judged by learners of English as a foreign language.