Readability Score Calculator
Flesch Reading Ease, Flesch–Kincaid grade, Gunning Fog, SMOG, Coleman–Liau and ARI for any text, with the word, sentence and syllable counts behind each shown.
Six readability scores with their published formulas, the counts behind them, Flesch’s own band for the score, and the hardest words so the syllable heuristic can be checked.
Example: “The quick brown fox jumps over the lazy dog. It was a sunny day.” has 14 words, 2 sentences and 17 syllables: Flesch Reading Ease 97.0 (very easy), Flesch–Kincaid grade 1.5, Gunning Fog 2.8.
Six formulas,
three counts.
What each score measures, how the counts are made, and where the syllable heuristic goes wrong.
The formulas
All six are published linear formulas on a few counts. Flesch Reading Ease (1948) = 206.835 − 1.015 × words per sentence − 84.6 × syllables per word, higher meaning easier, with Flesch's own bands from “very easy” to “very difficult”. Flesch–Kincaid (1975), Gunning Fog (1952), SMOG (1969), Coleman–Liau (1975) and ARI (1967) all estimate a US school grade: Flesch–Kincaid and Fog from sentence length and syllables (Fog and SMOG count “complex” words of three or more syllables), Coleman–Liau and ARI from letters or characters per word instead of syllables. The exact coefficients are in the engine and the provenance line.
Counting
Words are runs of letters and digits (contractions count once). Sentences end at . ! ? followed by a space and a non-lowercase character, so “e.g. this” does not split. Syllables are counted by a heuristic: groups of vowels, a silent final e dropped (“cake” = 1) except after a consonant + le (“table” = 2), minimum one. It gets most words right and some wrong — “science” counts as 1 — which is why the hardest words are listed: if one looks wrong, the syllable-based scores are off by that much.
What a score means
These formulas measure surface features — sentence length and word length — not clarity, structure or whether the reader knows the subject. They were calibrated on passages of about 100 words (SMOG on 30 sentences); very short samples swing widely and the page says so. Use the scores to compare drafts, not to certify one. Nothing leaves the browser; the same four anonymous usage counts as the rest of the site apply.
SOURCES
- Flesch, R. (1948). A new readability yardstick. Journal of Applied Psychology 32(3), 221–233 — Reading Ease formula and bands
- Kincaid, J. P. et al. (1975). Derivation of new readability formulas for Navy enlisted personnel. Naval Technical Training Command, Research Branch Report 8-75 — Flesch–Kincaid grade level
- McLaughlin, G. H. (1969). SMOG grading — a new readability formula. Journal of Reading 12(8), 639–646; Gunning (1952) Fog; Coleman & Liau (1975); Senter & Smith (1967) ARI
Last reviewed 19 September 2026. How results are checked: How we verify.