Automated Readability Index (ARI)

ARI was developed in 1967 for the US Air Force to run on early electronic typewriters — machines that could count characters but couldn't yet count syllables. Formula: 4.71 × (characters/words) + 0.5 × (words/sentences) − 21.43. Like Coleman-Liau, it sidesteps syllable counting. Its US grade-level output aligns reasonably well with Flesch-Kincaid for standard prose but can drift on texts with unusual word-length distributions (e.g., technical writing with many acronyms or lots of short function words).