The Powers-Sumner-Kearl formula estimates the U.S. grade level needed to read elementary-grade text. Pairs naturally with Spache and Dale-Chall.
Built and maintained by Paul Clark, Redmoon Software · Last verified · Sources
Use Powers-Sumner-Kearl for elementary text. It pairs naturally with Spache for K-4 readers and Dale-Chall for grades 4-8. Originally a simplified variant of Flesch designed for primary education.
PSK is one of three primary-grade formulas (with Spache and Dale-Chall). The three together provide consensus for elementary text. PSK is the simplest and fastest of the three.
Powers-Sumner-Kearl is a simplified Flesch variant from 1958: 0.0778 × avg sentence length + 0.0455 × syllables-per-100-words − 2.2029.
It outputs a grade level calibrated for primary education (grades 1-6).
Use alongside Spache and Dale-Chall for a primary-grade consensus.
Same inputs (sentence length + syllables) with different coefficients. PSK is calibrated for primary grades; FK extends through college.
For elementary text (grades 1-6), PSK is better calibrated. For older audiences, use Flesch-Kincaid.
In academic reading research, yes. In commercial writing, Flesch-Kincaid dominates. PSK shines as a third opinion for primary text.
Input
A 50-word elementary text with short sentences and one-syllable words.
Output
PSK grade 2.8 — primary.
Short sentences (avg 8 words) and low syllables-per-100 (110) place this firmly in early elementary range.
Powers, Sumner and Kearl did not invent a readability measure in 1958. They took four existing ones — including Flesch and Dale–Chall — and refitted their coefficients against a single common criterion, so that the four could be compared on equal terms rather than each reporting against its own calibration.
What this tool implements is that recalculated variant. It is fitted to primary-grade material, which is why it produces a much narrower range of grade levels than the formulas it derives from, and why it looks oddly optimistic on adult prose.
Because the refitting used a criterion set of children's reading material, the model has little to say above about sixth grade — the outputs bunch up. A university paper and a broadsheet editorial can land within a grade of each other, which is not a useful distinction.
Its value is historical and comparative: it is the clean way to see how much of the disagreement between classic formulas is genuine and how much is just different calibration. For a working readability judgement on adult text, use one of the formulas fitted to adult text.
The method behind this tool, so you can check it rather than take it on trust.
Powers, R.D., Sumner, W.A. & Kearl, B.E. (1958). “A recalculation of four adult readability formulas.” Journal of Educational Psychology, 49(2), 99–105.
Recalibrated four earlier formulas against a common criterion; this tool implements the recalculated variant.
Classic 0–100 readability score.
Readability scoresU.S. grade level for your text.
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