Flesch-Kincaid Readability Calculator
Flesch-Kincaid has been the standard readability benchmark since 1948, scoring text by sentence length and average syllables per word. Paste any English passage and this tool instantly computes the two industry-standard metrics: Flesch Reading Ease (0–100, higher = easier) and Flesch-Kincaid Grade Level (an approximate US school grade). MS Word, Google Docs, US Navy training manuals and most governments' plain-language guidelines all use this same pair of formulas.
Please enter at least one English sentence (with letters and a terminator).
Words
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Sentences
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Syllables
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Complex words
—
3+ syllables
Flesch Reading Ease
—
—Higher = easier (0–100, can exceed 100)
Flesch-Kincaid Grade Level
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Approximate US school grade
Details
- Avg words per sentence
- —
- Avg syllables per word
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Syllable counts use the standard heuristic algorithm (strip silent e, count vowel groups). This is accurate for the vast majority of English words but can be off by ±1 syllable on irregular words such as "create" or "ocean". Non-Latin scripts (Chinese, Japanese, Arabic) are not measurable with this index.
Formula
FRE = 206.835 − 1.015 × (words / sentences) − 84.6 × (syllables / words) FKGL = 0.39 × (words / sentences) + 11.8 × (syllables / words) − 15.59
- · Flesch Reading Ease: 90–100 = 5th-grade level, 60–70 = "Plain English" (8th–9th grade), below 30 = "Very Difficult."
- · Flesch-Kincaid Grade Level maps directly to US school grade — e.g. 8.0 ≈ start of 8th grade.
- · The formulas are calibrated for English only. Languages without syllabic structure (Chinese, Japanese kanji) cannot be scored meaningfully.
- · Syllable counts use the standard heuristic (strip silent e, count vowel groups) — the same approach used by textstat, readability-score and MS Word.
- · Irregular words such as "create" or "ocean" can be off by ±1 syllable; longer passages average out the noise.
- · Plain-language guideline: aim for FRE ≥ 60 (FKGL ≤ 9) so general readers can follow easily.
- · Sources: Flesch R., J. Applied Psychology 32 (1948); Kincaid et al., Naval Training Research Branch Report 8-75 (1975).
Frequently asked
What score counts as "easy to read"?
Flesch himself recommended a Reading Ease of at least 60 (≈ 8th–9th grade, FKGL ≤ 9) for general audiences. US plain-language regulations for insurance, tax and health documents typically require FRE ≥ 60 or FKGL ≤ 8. Academic journals and legal text usually land below 30 FRE and above grade 13.
FRE or FKGL — which should I use?
They are two scales for the same underlying ratio. Reading Ease (0–100, higher = easier) gives an intuitive score you can target internally. Grade Level expresses the same thing as a US school grade — useful when explaining to non-technical stakeholders ("I'm writing for an 8th-grader"). Cross-check both to avoid being misled by an outlier sentence.
Does it work for Chinese?
Not meaningfully. Flesch-Kincaid assumes Latin-alphabet words with countable syllables. Chinese is logographic — every character is roughly a morpheme, with no syllable structure to measure in the same way. For Chinese readability, look at indices designed for it (e.g. SCRI, Chinese Readability Index Explorer) or measures based on character frequency and sentence length.
How are syllables counted? Why does "create" sometimes come out as 1?
We use the same heuristic as textstat / readability-score / MS Word: lowercase the word, strip a silent "e" / "es" / "ed" preceded by a consonant, then count vowel groups (e.g. "ea" = 1 group). The algorithm matches dictionary syllable counts for most English words but undercounts words containing diphthongs that should split (-eate, -iate, -ion). The error averages out across paragraphs and produces results well within Flesch-Kincaid's intended use as a rough indicator.
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