The two formulas
This tool computes both classic Flesch measures from three counts: words, sentences and syllables. Let W be words per sentence and S be syllables per word.
- Flesch Reading Ease (Rudolf Flesch, 1948):
206.835 - 1.015 x W - 84.6 x S, clamped here to the range 0 to 100. Higher means easier. - Flesch-Kincaid Grade Level (Kincaid and colleagues, US Navy, 1975):
0.39 x W + 11.8 x S - 15.59, floored at 0 so it never goes negative.
The label under the numbers uses the standard Flesch bands: 90 and above is "very easy", 60 to 69 is plain English, 30 to 49 is difficult, and below 30 is very difficult.
Worked example
Take: Good writing uses short sentences. Plain words help readers. Long sentences with many clauses and abstract vocabulary make comprehension harder, so editors often split them.
| Measure | Value |
|---|---|
| Words | 25 |
| Sentences | 3 |
| Syllables (estimated) | 42 |
| Words per sentence | 8.33 |
| Syllables per word | 1.68 |
| Reading ease | 206.835 - 8.46 - 142.13 = 56.2 |
| Grade level | 3.25 + 19.82 - 15.59 = 7.5 |
Notice that the ease score of 56.2 lands in the "fairly difficult, 10th-12th grade" band while the grade-level formula says 7.5. The two formulas weight the same inputs differently, and the band names come from Flesch's own table, so they can disagree on short samples. Treat them as two rough indicators.
How syllables and sentences are counted
Words are runs of Unicode letters and digits (with internal straight or curly apostrophes), so "café" is one word and a number such as 2024 counts as one word. For syllables, accents are stripped first, a number or a word in a non-Latin script counts as 1, and a word of three letters or fewer counts as 1. Longer words lose a trailing es, ed or silent e, drop a leading y, and then each group of one or two consecutive vowels (a, e, i, o, u, y) counts as a syllable. Sentence breaks come from a ., ! or ? that is followed by a space, a newline or nothing at all. With no end punctuation at all, the text counts as one sentence.
Where the estimate goes wrong
- Rules like these miscount some common words: "created" is counted as 1 syllable (it has 3), "business" as 3 (2), "beautiful" as 4 (3), "science" as 1 (2) and "idea" as 2 (3).
- Headings and bullet lists without full stops merge into the next sentence, which inflates words per sentence and lowers the ease score. Add a full stop to each line.
- Abbreviations such as "e.g. " and "Dr. " each add a false sentence, which makes text look easier than it is.
- Very short or very long samples produce extreme results. A tiny text can score above 100 before clamping, and dense jargon can fall below zero, as one eight-word sentence of long words does.
- The formulas were designed for English. Accented Latin letters are now read as part of the word, but the syllable rules are English ones, and non-Latin scripts count one syllable per word, so scores for other languages are only a rough guide.
To find which words are repeated, see the word frequency counter, and for basic length figures the word counter.