The Dale–Chall formula identifies the percentage of unfamiliar words and produces a grade-level score.
Built and maintained by Paul Clark, Redmoon Software · Last verified · Sources
Use Dale–Chall when your audience is children, English learners, or general adults reading material outside their expertise. Because it scores familiarity (not syllable count), it catches problems that other formulas miss — like "epistemology" vs. "knowledge".
Dale–Chall is the only mainstream formula that scores vocabulary familiarity. Compared to Flesch–Kincaid it is much more sensitive to word choice and much less sensitive to sentence length. Pair it with Flesch–Kincaid for a balanced view.
The Dale-Chall formula compares your text against a fixed list of approximately 3,000 "familiar" words that 80% of 4th-graders know.
Words not on the list are considered "difficult." The formula combines the percentage of difficult words with average sentence length.
This implementation uses the New Dale-Chall (1995) revision with 2,942 words, courtesy of the open-source `dale-chall` package.
A list of approximately 3,000 words that 80% of 4th graders are familiar with. We use the New Dale-Chall (1995) revision with 2,942 words.
Dale-Chall is conservative. Suffixes (-ed, -ing) are stripped before matching, but uncommon spellings, regional words, and most proper nouns count as unfamiliar.
A raw Dale-Chall score of 5.0–5.9 means easily understood by 5th–6th graders. Marketing and consumer text typically target 6.0–6.9.
Input
The pedagogical efficacy of constructivist methodologies remains contested.
Output
Dale–Chall Score: 11.4 — College graduate.
Six of seven words are not on the Dale–Chall familiar-words list. The high "unfamiliar word" ratio combines with the single long sentence to produce a graduate-level score.
Dale–Chall is the odd one out in this collection, and the most interesting. Every other formula infers difficulty from a shape — how long the words are, how many syllables, how long the sentences. Dale–Chall asks a different question: is this word one that a fourth-grade reader actually knows? It answers by checking each word against a list of about 3,000 words established as familiar to fourth graders.
That is why it handles the case the shape-based formulas get wrong. "Grandmother" is eleven letters and three syllables, and every syllable-based formula treats it as hard; it is on the familiar list, so Dale–Chall does not. "Writ" is four letters and one syllable, and no shape-based formula flags it; it is not on the list, so Dale–Chall does.
The score is 0.1579 × (percentage of unfamiliar words) + 0.0496 × average sentence length, with an important discontinuity: if more than 5% of words are unfamiliar, a further 3.6365 is added. That step is in the original formula, and it means a document sitting just either side of 5% can jump most of a grade level for a small change in vocabulary.
Matching is not literal. Before a word is judged unfamiliar, common inflections are stripped — plural "-s", "-ed", "-ing", "-ly", "-er", "-est" and possessives — so "walked", "walking" and "walks" all match "walk" on the list rather than counting as three unfamiliar words. Anything beginning with a digit is treated as familiar, on the basis that numbers are read rather than looked up.
The words this tool reports as difficult are therefore worth reading rather than trusting blindly. Proper nouns are the largest category of false positives: names of people, places and products are not on a list of general vocabulary and will be flagged every time, even though a reader has no trouble with them in context.
Used well, the list of flagged words is more useful than the score. It is a concrete, per-word edit list, which no other formula here produces.
The method behind this tool, so you can check it rather than take it on trust.
Dale, E. & Chall, J.S. (1948). “A Formula for Predicting Readability.” Educational Research Bulletin, 27(1), 11–20.
The original formula, scoring against a list of words familiar to fourth-grade readers.
Chall, J.S. & Dale, E. (1995). Readability Revisited: The New Dale–Chall Readability Formula. Brookline Books.
The revised formula and the expanded familiar-word list this tool scores against.
Classic 0–100 readability score.
Readability scoresU.S. grade level for your text.
Readability scoresPenalises complex (3+ syllable) words.
Readability scoresHealth & medical text grade level.