Dale-Chall Readability Formula
A readability index that combines sentence length with a frequency-list operationalisation of word difficulty. Where Flesch, Fog, and SMOG approximate word difficulty by syllable count, Dale-Chall measures it directly: any word not on a list of high-frequency familiar words is difficult. Originally published by Edgar Dale and Jeanne Chall in 1948 as a competitor to Flesch; comprehensively revised in 1995 as the New Dale-Chall with an expanded 3,000-word familiar list and updated coefficients.
The 1995 New Dale-Chall formula
If the percentage of difficult words exceeds 5%, the formula adds a 3.6365 correction. The raw score maps to a grade-level band:
- 4.9 or below: easily understood by 4th grade and below
- 5.0–5.9: 5th–6th grade
- 6.0–6.9: 7th–8th grade
- 7.0–7.9: 9th–10th grade
- 8.0–8.9: 11th–12th grade
- 9.0–9.9: college (13th–15th grade)
- 10.0+: college graduate
The 1995 revision was published as Chall and Dale's book Readability Revisited: The New Dale-Chall Readability Formula. The revision rebased the formula on a new corpus of grade-calibrated passages, expanded the familiar-word list from the original ~763 words (Dale 1948) to 3,000 words, and updated the coefficients accordingly.
The familiar-word list
The 3,000-word New Dale-Chall list is empirically derived: it is the set of words that a sample of fourth-grade American students could reliably understand on a standardised test. Fifth-graders are expected to know roughly 80% of the list; by sixth grade students should know all of it. Words on the list — and their regular inflections — count as familiar. Everything else counts as difficult.
The list explicitly handles inflection. Run, runs, running, and ran all count as familiar if run is on the list. Proper nouns and compound words built from familiar parts also count as familiar. This handling fixes one of the issues that complicates Fog's complex-word rules.
Why frequency-based readability is different
Dale-Chall is the only major readability formula whose word-difficulty predictor is empirically grounded rather than surface-mathematical. Syllable counts are a proxy for difficulty; frequency-list membership is a direct measurement (against a specific population). This makes Dale-Chall:
- More sensitive to vocabulary than syllable-count formulas. A short Latinate word like
ceaseregisters as difficult in Dale-Chall while passing through Flesch and Fog unmarked. - Less sensitive to syntactic complexity than its competitors. Dale-Chall has only one sentence-length term and a small coefficient.
- Population-anchored. The familiar list is calibrated to US fourth-graders. Applied to L2 English texts, the bands shift: a word familiar to a US fourth-grader may be unfamiliar to a B1 ESL learner, and a word unfamiliar to a US fourth-grader (
molecule) may be high-frequency in academic L2 contexts.
Use in ELT and test design
For ELT use Dale-Chall is most valuable when vocabulary band, not syntactic complexity, is the calibration target. Graded readers, ESL textbooks, and frequency-aligned reading materials are the natural fit: the question is what proportion of words sit outside the target band, which is exactly what Dale-Chall measures.
The L2 caveat matters. Dale-Chall is calibrated for native-speaker comprehension by US fourth-graders, not for CEFR bands. For CEFR-aligned test passage sourcing, use a CEFR-anchored vocabulary profiler (English Vocabulary Profile, CEFR-J) rather than Dale-Chall, and treat Dale-Chall as a coarse complement, not a primary index. The principle is sound; the population is wrong.
Why Dale-Chall and Flesch sometimes disagree sharply
The two formulas can give opposing verdicts on the same text. A text with short sentences but rare-but-short words (opt, plea, gist, wane) reads easy by Flesch and difficult by Dale-Chall. A text with long sentences but common-and-long words (responsibility, understanding, community) reads difficult by Flesch and easy by Dale-Chall. This is the predictable signature of formulas that operationalise word difficulty differently. When the two agree on a text, the readability assessment is robust; when they disagree, the disagreement itself is the diagnostic.
Key References
- Dale, E. & Chall, J. S. (1948). A formula for predicting readability. Educational Research Bulletin, 27(1), 11–20, 28.
- Chall, J. S. & Dale, E. (1995). Readability Revisited: The New Dale-Chall Readability Formula. Brookline Books.
- DuBay, W. H. (2004). The Principles of Readability. Impact Information.
See Also
- Readability: the umbrella construct
- Frequency Lists / High-frequency and Low-frequency Words: the resource family Dale-Chall's familiar-word list belongs to
- Flesch Reading Ease / Flesch-Kincaid Grade Level / Gunning Fog Index / SMOG: the syllable-based competitors Dale-Chall is most often reported against