The Spache Readability Formula scores text against a list of familiar primary-grade words. Designed for K-4 reading material.
Built and maintained by Paul Clark, Redmoon Software · Last verified · Sources
Use Spache for any text aimed at K-4 readers — primary readers, beginning ESL, picture books, learn-to-read content. It's the formula educators most often request for grade 4 and below.
Spache and Dale-Chall both use familiar-words lists, but Spache targets younger readers (K-4) and Dale-Chall targets grades 4+. Use Spache for primary, Dale-Chall for everything else.
The Spache Readability Formula was developed in 1953 specifically for primary-grade text (K-4).
It scores against a list of approximately 1,000 words familiar to elementary readers, combined with sentence length: grade = 0.121 × avg sentence length + 0.082 × % unfamiliar + 0.659.
Best used to evaluate beginning readers, picture books, and ESL primary material. Above grade 4, switch to Dale-Chall.
Spache for K-4 reading material. Dale-Chall for grade 4+. They use different familiar-words lists.
The Spache list dates to 1953 — modern children's vocabulary may not match. Suffix stripping helps but isn't perfect.
Grade 1-2 for early readers, 3-4 for primary independent reading. Above grade 4, use a different formula.
Input
"The dog ran fast across the green field."
Output
Spache grade 1.4 — primary.
All eight words are in the Spache familiar-words list and the sentence is short. Suitable for grade 1–2 readers.
Spache is the formula to use for primary-grade material, and the reason is that the rest of this collection is unreliable there. Formulas fitted on adult and secondary text compress badly at the bottom of their range: they will happily report "grade 2.1" and "grade 2.8" for texts that differ in ways they were never calibrated to distinguish.
Spache uses a familiar-word list like Dale–Chall, but a different and shorter one aimed at early readers, combined with average sentence length. It was published in 1953 specifically for material below about fourth grade.
Above roughly fourth grade Spache stops discriminating — everything is familiar and the score flattens. If your text scores at the top of its range, switch to Dale–Chall, which uses the same familiar-word idea calibrated for older readers.
The familiar-word list is also of its time. Vocabulary that was common to children in the 1950s is not identical to what is common now, in either direction, and the list has no entries for anything invented since. Treat flagged words as candidates to review rather than verdicts.
The method behind this tool, so you can check it rather than take it on trust.
Spache, G. (1953). “A New Readability Formula for Primary-Grade Reading Materials.” The Elementary School Journal, 53(7), 410–413.
Calibrated for material below fourth grade, where the other formulas are unreliable.
Classic 0–100 readability score.
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