Flesch-Kincaid Readability Calculator
Estimate the US school grade level required to read your text.
Paste English prose. The tool estimates Flesch-Kincaid grade level and Flesch reading ease.
How is this calculated?
Flesch-Kincaid grade level: 0.39 x (words / sentences) + 11.8 x (syllables / words) - 15.59. Flesch reading ease: 206.835 - 1.015 x (words / sentences) - 84.6 x (syllables / words). Syllables are estimated by counting groups of vowel letters in each lowercased word, with a final silent-e adjustment. Counts are approximate; long compound words and proper nouns can shift the syllable estimate. Source: Kincaid et al. (1975), Naval Air Station Memphis.
About Flesch-Kincaid readability
Flesch-Kincaid is a pair of formulas, developed by Rudolph Flesch and J. Peter Kincaid for the US Navy in 1975, that score English prose on sentence length and word complexity. The Grade Level output maps to a US school grade; the Reading Ease output is a 0 to 100 score where higher is easier.
How it works
Both formulas use only three measurable counts: sentences, words, and syllables. No semantics, no part of speech, no vocabulary list. Cheap to compute, easy to game, but a useful proxy.
ASL = Average Sentence Length = words / sentences ASW = Average Syllables per Word = syllables / words FRE (Flesch Reading Ease) = 206.835 - 1.015 x ASL - 84.6 x ASW FKGL (Flesch-Kincaid Grade Level) = 0.39 x ASL + 11.8 x ASW - 15.59
- Sentence count: occurrences of
. ! ?followed by space or end-of-text. - Word count: tokens matching
\b[\w'-]+\b; contractions and hyphenated words count as one. - Syllable count: groups of vowel letters per lowercased word with a silent-e adjustment. Roughly 85 to 92 percent accurate vs the CMU Pronouncing Dictionary.
- FRE interpretation: 90 to 100 very easy (5th grade); 60 to 70 plain English (8th to 9th); 30 to 50 college; below 30 college graduate and professional.
Worked example
Score the sentence "The quick brown fox jumps over the lazy dog. Readability matters." (two sentences, twelve words, sixteen syllables):
- Sentence count: 2.
- Word count: 12.
- Syllable count: the (1), quick (1), brown (1), fox (1), jumps (1), over (2), the (1), lazy (2), dog (1), readability (6), matters (2) = 19 by the pattern algorithm.
- ASL: 12 / 2 = 6.0 words per sentence.
- ASW: 19 / 12 = 1.583 syllables per word.
- FRE: 206.835 - (1.015 x 6.0) - (84.6 x 1.583) = 206.835 - 6.09 - 133.92 = 66.83.
- FKGL: (0.39 x 6.0) + (11.8 x 1.583) - 15.59 = 2.34 + 18.68 - 15.59 = 5.43.
Reading ease interpretation table
| FRE score | Grade band | Difficulty | Example text |
|---|---|---|---|
| 90 to 100 | 5th grade | Very easy | Children's books, conversational fiction |
| 80 to 90 | 6th | Easy | Reader's Digest, mass-market magazines |
| 70 to 80 | 7th | Fairly easy | Tabloid news, top-of-funnel marketing |
| 60 to 70 | 8th to 9th | Plain English | NYT, Wall Street Journal, federal plain-language guidance |
| 50 to 60 | 10th to 12th | Fairly difficult | The Atlantic, popular science |
| 30 to 50 | College | Difficult | Harvard Business Review, academic textbooks |
| 10 to 30 | College grad | Very difficult | Law reviews, scientific journals |
| 0 to 10 | Professional | Extremely difficult | Insurance policies, IRS regulations |
Common mistakes
- Treating FK grade as truth. The formula was calibrated on Navy training manuals in 1975 and does not know whether your text makes sense. It only knows length.
- Gaming with short sentences only. You can drop a passage to grade 4. But. Choppy. Sentences. Score well yet read poorly.
- Forgetting genre fit. Plain-language US federal guidance targets grade 8 for public-facing content. Legal contracts run grade 14 to 18 by design.
- Trusting pattern-based syllable counts on proper nouns. "Jalapeno" or "Ouagadougou" can throw the count off by 1 to 2 syllables. Edit famous names out before scoring or use the CMU dictionary for production scoring.
- Comparing across languages. Flesch-Kincaid is calibrated on English. Spanish, French, and German have their own variants (Fernandez-Huerta, Gunning Fog, Lasbarhetsindex) with different constants.
- Scoring marketing copy and instructions the same. Step-by-step instructions need shorter sentences and concrete verbs (grade 6 to 8). Narrative or persuasive copy tolerates grade 9 to 11 without losing the reader.
Related tools and glossary
Frequently asked questions
What is a good Flesch reading ease score?
60 to 70 is plain English suitable for 13 to 15 year olds and most general audiences. The Wall Street Journal averages around 55, the New York Times around 60, and Reader's Digest around 65. Insurance contracts and legal text often score below 30 (very difficult).
How accurate are syllable counts?
Pattern-based syllable counting (groups of vowel letters with a silent-e adjustment) is roughly 85 to 92 percent accurate on common English words. Proper nouns, compound words, and loanwords (jalapeno, Bjork) skew higher. For peer-reviewed work, use the CMU Pronouncing Dictionary as the canonical source.
Why does my grade level seem too high?
Flesch-Kincaid rewards short sentences and short words. Long sentences with many polysyllabic Latinate words (utilize, implementation, comprehensive) inflate the grade. The fix is to shorten sentences to 15 to 20 words and prefer Anglo-Saxon synonyms (use, plan, full) where possible.
Should I aim for low grade level in all writing?
No. Match grade to audience. Plain-language guidelines for US federal agencies target 8th grade for public-facing content. Marketing email lands best at grade 6 to 8. Academic, legal, and scientific writing legitimately runs grade 12 to 16 because precision matters more than ease.
Sources
- Kincaid, J. Peter et al. (1975) Derivation of New Readability Formulas for Navy Enlisted Personnel, Research Branch Report 8-75, Naval Air Station Memphis.
- Flesch, Rudolf (1948) A New Readability Yardstick, Journal of Applied Psychology 32.
- US Plain Writing Act of 2010 and Federal Plain Language Guidelines (2011).
- Carnegie Mellon University (2014) CMU Pronouncing Dictionary, syllable ground truth.