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Four readability measures for any passage, against 46 bestsellers and the band for memoir, spirituality, self-help and business.
The median non-fiction bestseller scores 60.4 on Flesch Reading Ease, about a ninth-grade reading level. That is the finding of The Anatomy of a Bestseller (47 books; 46 measured, the Bhagavad-gita being unscoreable). The middle half of its books score 51.5 to 66.7. Paste a passage to see where yours sits against that band and your genre’s.
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Reading ease, grade level, sentence length and word length, each against the middle half of bestsellers and of your genre. These are the Flesch bands:
How it works
To check readability of text, paste at least 100 words from one chapter. The checker runs in your browser; nothing you paste is sent or stored.
Flesch Reading Ease (higher is easier), Flesch-Kincaid grade, average words per sentence and average syllables per word.
Each measure is set against the middle half of all 46 bestsellers and of five memoir, 16 spirituality, nine self-help and nine business titles.
Your score’s gap from the median bestseller splits into a part from sentence length and a part from word length. Change the bigger one first.
Method and sources
Flesch Reading Ease is 206.835 − 1.015 × words per sentence − 84.6 × syllables per word (Flesch, 1948). Higher is easier. The Flesch-Kincaid grade is 0.39 × words per sentence + 11.8 × syllables per word − 15.59, a US reading level expressed as a school grade. Kincaid and colleagues derived it for the US Navy in 1975.
This reading level checker counts syllables by rule rather than from a dictionary. Its scores can differ by a few points from another readability test tool or a full report. Fragments of one or two words, such as headings, do not count as sentences.
The bands are the middle half (25th to 75th percentile) of each group’s books, from the study’s scorecard and its genre playbooks. The study scored the reading level of books as a whole, averaging each chapter weighted by its length. One passage swings further than a book’s average, so check readability level on passages from several chapters before you rewrite.
| What | Figure | Source | Checked |
|---|---|---|---|
| Flesch Reading Ease, median bestseller | 60.4 (middle half 51.5–66.7) | The Anatomy of a Bestseller, scorecard | |
| Flesch-Kincaid grade, median bestseller | 9.4 (middle half 8.3–11.3) | The Anatomy of a Bestseller, scorecard | |
| Words per sentence; syllables per word | 16.0 (14.1–18.4); 1.53 (1.47–1.62) | The Anatomy of a Bestseller, scorecard | |
| Flesch Reading Ease, middle half by genre | memoir 62.1–80.2, spirituality 57.4–69.6, self-help 56.6–63.5 and business 51.4–58.2 | The Anatomy of a Bestseller, genre playbooks | |
| Flesch Reading Ease formula | 206.835 − 1.015 × words per sentence − 84.6 × syllables per word | Flesch (1948), A new readability yardstick, Journal of Applied Psychology 32(3), 221–233 | |
| Flesch-Kincaid grade formula | 0.39 × words per sentence + 11.8 × syllables per word − 15.59 | Kincaid, Fishburne, Rogers and Chissom (1975), Derivation of New Readability Formulas for Navy Enlisted Personnel, Research Branch Report 8-75 |
Quick answers
For a non-fiction book, 51.5 to 66.7: the middle half of 46 bestsellers in the study, with the median at 60.4. Genre moves the band: memoir sits at 62.1 to 80.2 and business at 51.4 to 58.2. Higher is easier; the study’s advice is to aim for the middle half of your genre.
For adult non-fiction, the reading level of a book should be about ninth grade. The median bestseller in the study scores 9.4 on the Flesch-Kincaid grade, and the middle half 8.3 to 11.3. Memoir runs lowest, at a median of 8.3, and business highest, at 10.5.
Multiply the average words per sentence by 0.39 and the average syllables per word by 11.8, add them, and subtract 15.59. The result is a US school grade. J. Peter Kincaid and colleagues derived it in 1975 by recalculating Rudolf Flesch’s 1948 Reading Ease formula against tests of 531 Navy enlisted personnel.
Shorten words before you shorten sentences. In the study, memoir’s plain vocabulary puts it about 14 Flesch points above the median book, and its shorter sentences only about 3 more. In the formula, 0.1 fewer syllables a word adds 8.5 points; one word fewer a sentence adds 1.
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The study
The Anatomy of a Bestseller
What 47 non-fiction classics reveal about writing that works.
Guide
Is my book ready to publish?
Ten checks for a finished draft, with the study’s ranges as the numbers to hit.
Guide
The self-editing checklist
Seven editing passes, each with a test taken from the scorecard.
Guide
How to write a memoir
How the five memoirs in the study open, are built and run long.
Guide
How to write a Christian book
What the 17 spirituality titles share in length, reading level and openings.
Guide
Business books, measured
Nine business bestsellers, with the narrowest length range of any genre.
Guide
Self-help books, measured
Nine self-help bestsellers and the chapter pattern they share.
Published . Figures checked 18 October 2026.
