Alternate Readability Formulas (SMOG / Coleman-Liau / Gunning Fog / ARI)
Four additional reading-grade formulas beyond Flesch-Kincaid.
Example
You enter
- Text to score (paste or type a paragraph) The quick brown fox jumps over the lazy dog. This sentence contains words of varying length. Some are short. Others are considerably longer. The readability formulas were developed for the United States Navy by Kincaid and colleagues in 1975. Their goal was to estimate the grade level needed to read a passage of running prose. The formulas remain widely used today by educators and writers.
You get
- Sentences 7
Details, formula, and sources
SMOG (McLaughlin 1969), Coleman-Liau (1975), Gunning Fog (1952), and ARI (Smith + Senter 1967). Same text input as Y.1.
SMOG = 1.043 * sqrt(polysyllables * (30/sentences)) + 3.1291. Coleman-Liau = 0.0588 * L - 0.296 * S - 15.8 (L = letters/100 words; S = sentences/100 words). Gunning Fog = 0.4 * (words/sentences + 100 * complex/words). ARI = 4.71 * (chars/words) + 0.5 * (words/sentences) - 21.43.
SMOG per McLaughlin, 'SMOG Grading: A New Readability Formula,' Journal of Reading 12:8 (1969). Coleman-Liau per Coleman + Liau, 'A computer readability formula designed for machine scoring,' Journal of Applied Psychology 60:2 (1975). Gunning Fog per Gunning, 'The Technique of Clear Writing' (1952). ARI per Smith + Senter, 'Automated Readability Index,' AMRL-TR-66-220 (1967), public-domain federal publication.
AMRL-TR-66-220 free at dtic.mil. The McLaughlin, Coleman-Liau, and Gunning papers are widely summarized in any introductory linguistics or composition reference.
Estimate only. Readability formulas and similar metrics are derived from a representative population and have known edge-case noise. The classroom teacher governs final text selection, grade placement, and assessment decisions.
Field names used by the API: text, sentences
- Polysyllable any word with 3+ syllables per the deterministic counter (SMOG and Gunning Fog 'complex word')McLaughlin 1969 / Gunning 1952
- Validity range SMOG validated against ~30 sentence passages; <100 words flagged as unreliableMcLaughlin 1969 §3