Readability Score Calculator

Flesch-Kincaid is a family of readability formulas that estimate text difficulty from sentence length and syllable count. The Reading Ease score runs 0–100 (higher is easier; 60–70 targets eighth grade); the Grade Level score corresponds to US school grade.

From word count, sentence count, and syllable count, the calculator produces both scores. Input the raw text or paste pre-counted statistics. Long sentences and polysyllabic words push grade level up.

The formulas were developed by Rudolf Flesch in the 1940s and refined by J. Peter Kincaid in 1975 for the US Navy to assess training manual difficulty. Reading Ease = 206.835 - 1.015 × (words/sentences) - 84.6 × (syllables/words). Grade Level = 0.39 × (words/sentences) + 11.8 × (syllables/words) - 15.59. The constants were calibrated empirically against texts of known reading level. Because the formulas only use sentence length and syllable count, they reward short sentences and short words and have nothing to say about vocabulary difficulty, syntactic complexity, or coherence. A sentence of jargon-free Anglo-Saxon monosyllables scores easy; the same idea expressed with Latinate vocabulary scores hard.

A worked example. Take this sentence: 'The cat sat on the mat.' Six words, one sentence, six syllables. Reading Ease = 206.835 - 1.015 × 6 - 84.6 × 1.0 = 206.835 - 6.09 - 84.6 = 116.1. Capped at 100, it's the easiest possible. Grade Level = 0.39 × 6 + 11.8 × 1.0 - 15.59 = 2.34 + 11.8 - 15.59 = -1.45. Negative grade level means below first grade, which is just the formula's edge case. A more realistic example: a 200-word paragraph with 12 sentences (16.7 words per sentence) and 320 syllables (1.6 per word). Reading Ease = 206.835 - 1.015 × 16.7 - 84.6 × 1.6 = 206.835 - 16.95 - 135.36 = 54.5. Grade Level = 0.39 × 16.7 + 11.8 × 1.6 - 15.59 = 6.51 + 18.88 - 15.59 = 9.8. So roughly a 10th grade reading level — typical for serious magazine writing.

Limitations and pitfalls. The formulas are English-specific and sentence-length-biased. Optimizing too hard for a low grade level produces choppy, telegraphic prose that's actually harder to parse because it loses connective tissue between ideas. Heuristic syllable counters (count vowel groups with adjustments for silent e, le endings) are right 80 to 90 percent of the time on English. Errors average out over long passages but can skew short passages noticeably. The score doesn't measure whether the reader can follow the argument, only whether the surface form is mechanically simple. Plain Language guidelines (US plain.gov, UK gov.uk style) target Reading Ease 60 to 70 for general audiences, equivalent to 8th to 9th grade. Technical documentation often scores 30 to 50 because the vocabulary requires it; that's not a defect.