The Dale-Chall readability formula was developed by Edgar Dale and Jeanne Chall in 1948, with an updated version (New Dale-Chall) in 1995. It measures text difficulty by comparing words against a list of about 3,000 familiar words known to 4th graders. Words not on this list are considered "difficult." The formula produces a score that maps to grade levels.

The Dale-Chall formula is: Score = 0.1579 × (difficult_words/total_words × 100) + 0.0496 × (words/sentences). If more than 5% of words are difficult, 3.6365 is added to the score. We count words not on the Dale-Chall familiar words list, then apply this formula to produce a grade-level interpretation.

A score of 4.9 or lower indicates 4th grade or lower—very easy to read. Scores of 5.0–5.9 are 5th–6th grade (easy), 6.0–6.9 are 7th–8th (fairly easy), 7.0–7.9 are 9th–10th (fairly difficult), 8.0–8.9 are 11th–12th (difficult), and 9.0+ is college level. For general audiences, aim for 6.9 or lower.

The Dale-Chall familiar words list contains approximately 3,000 words that 80% of 4th-grade students could recognize. Words on this list are considered "easy"; words not on the list are "difficult." The list was compiled through research and is used to measure vocabulary difficulty in texts.

Dale-Chall uses a vocabulary-based approach (familiar vs. difficult words), while Flesch-Kincaid counts syllables and sentence length, and SMOG focuses on polysyllabic words. Dale-Chall is useful when you want to assess vocabulary difficulty specifically, whereas Flesch-Kincaid and SMOG emphasize structural complexity.