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Supported Metrics

Not sure which metric to use? The Choosing a Metric guide explains the differences.

readscore supports nine readability formulas:

  • ARI (Automated Readability Index) — Character-based formula; reliable on technical documents; includes age ranges
  • Coleman-Liau — Character-based formula; letters only; consistent results at scale
  • Dale-Chall — Word-list formula; validated for educational and health materials; grades 4+
  • Flesch Reading Ease — 0–100 ease score (higher = easier); most widely cited formula
  • Flesch-Kincaid — US grade level; same inputs as Flesch; targets 75% comprehension
  • Gunning Fog — Years of education needed; counts polysyllabic words; good for business prose
  • Linsear Write — Weighted syllable formula from the Bureau of Land Management (1966)
  • SMOG — 30-sentence polysyllabic word count; targets 100% comprehension; health literacy standard
  • Spache — Word-list formula for grades 1–3 only

Each metric provides a score and a grade_level (or grade_levels for more granular ranges). Some metrics provide additional data, like ages for ARI or ease for Flesch.