What is the Flesch Reading Ease score?

The Flesch Reading Ease (FRE) formula was developed by Rudolf Flesch in 1948. It outputs a score from 0 to 100 using the formula: FRE = 206.835 - 1.015 * (words / sentences) - 84.6 * (syllables / words). Higher scores mean easier text. A score of 60-70 is considered plain English and is suitable for most public-facing content. A score below 30 is considered very difficult and requires college-graduate-level reading skills.

What is the Flesch-Kincaid Grade Level and how does it differ from Reading Ease?

The Flesch-Kincaid Grade Level uses the same inputs (sentence length and syllables per word) but outputs a US school grade level instead of a 0-100 score. The formula is: FK Grade = 0.39 * (words / sentences) + 11.8 * (syllables / words) - 15.59. A grade of 8 means an 8th-grader can understand the text. Reading Ease and FK Grade use the same linguistic signals but are calibrated differently; they always move in opposite directions (a higher ease score corresponds to a lower grade level).

What is the Coleman-Liau Index and why is it useful?

The Coleman-Liau Index calculates readability from letter counts rather than syllable counts, making it trivial to compute mechanically: CLI = 0.0588 * L - 0.296 * S - 15.8, where L is the average number of letters per 100 words and S is the average number of sentences per 100 words. Because syllable counting is error-prone for computer programs, the Coleman-Liau is popular in automated tools and closely tracks Flesch-Kincaid in practice.

What is the Dale-Chall Readability Score?

The Dale-Chall formula differs from the others because it uses a reference list of 3,000 words familiar to a typical 9th-grader. Words not on that list are counted as "hard." The formula is: Raw = 0.1579 * (hard words / total words * 100) + 0.0496 * (words / sentences). If more than 5% of words are hard, add 3.6365. Scores above 9 indicate college-graduate difficulty. Dale-Chall is considered one of the most accurate formulas for educational text because it directly measures vocabulary difficulty rather than proxying it through syllable count.

How accurate are readability formulas?

All readability formulas are statistical approximations. They measure proxies for difficulty (sentence length, syllable count, word frequency) rather than true comprehension. A short sentence full of technical jargon can score as easy when it is not. For best results, use the Consensus Grade (the mean of all seven grade-level indices) which smooths out the weaknesses of any single formula, and always combine the score with your own editorial judgement. Aim for Flesch Reading Ease above 60 for general audiences.

What does the hard-word highlighter mark?

The highlighter marks any word that is either polysyllabic (three or more syllables, which contributes to Gunning Fog and SMOG scores) or absent from the Dale-Chall familiar-word list. These are the words most likely to slow a reader down. Click "Highlight hard words" to see them, then decide whether a simpler alternative exists. Click the highlighted view to return to editing mode.

Reading Ease Checker

The Reading Ease Checker runs eight established readability formulas against any piece of text and returns a full score dashboard, a hard-word highlighter, and concrete improvement tips — all computed live in your browser without uploading anything.

How it works

Text readability is measured through linguistic proxies: sentence length (average words per sentence), syllable density (average syllables per word), vocabulary familiarity (presence in a known-word list), and letter count (characters per word). Each formula weights these signals differently and targets a different use-case.

The eight formulas

Flesch Reading Ease (Rudolf Flesch, 1948) outputs a score from 0 to 100. Higher is easier. The formula is:

FRE = 206.835 - 1.015 (words ÷ sentences) - 84.6 (syllables ÷ words)

A score of 60-70 is the plain-English target recommended by government style guides worldwide. Below 30 is very difficult.

Flesch-Kincaid Grade Level uses the same inputs but outputs a US school grade number:

FK = 0.39 (words ÷ sentences) + 11.8 (syllables ÷ words) - 15.59

Gunning Fog Index (Robert Gunning, 1952) penalises polysyllabic words (3+ syllables):

Fog = 0.4 [ (words ÷ sentences) + 100 (polysyllabic words ÷ words) ]

SMOG Index (G. Harry McLaughlin, 1969) uses a square-root extrapolation of polysyllable density:

SMOG = 1.043 √(polysyllables × 30 ÷ sentences) + 3.1291

Coleman-Liau Index uses letter counts — no syllable counting required:

CLI = 0.0588 L - 0.296 S - 15.8 (L = avg letters per 100 words; S = avg sentences per 100 words)

Automated Readability Index (ARI) emphasises character-to-word ratio:

ARI = 4.71 (chars ÷ words) + 0.5 (words ÷ sentences) - 21.43

Dale-Chall Readability Score cross-references a 3,000-word familiar-word list. Words outside that list are “hard.” If more than 5% of words are hard, a correction factor of 3.6365 is added. This makes it one of the most vocabulary-sensitive formulas.

Linsear Write Formula weights each word as 1 point (≤2 syllables) or 3 points (≥3 syllables), sums those points, divides by sentence count, and halves any result above 20.

The Consensus Grade shown in the dashboard is the arithmetic mean of all seven grade-level indices and gives a single, robust estimate that smooths the weaknesses of any individual formula.

Worked example

Take two versions of the same sentence:

“The utilisation of unnecessarily polysyllabic terminology in professional correspondence frequently engenders comprehension difficulties among the intended recipients.”
“Using long, rare words in business emails often confuses readers.”

Version 1 scores around Flesch 5 (very difficult, college graduate) and FK Grade 20+. Version 2 scores around Flesch 72 (fairly easy, 7th grade). Same message; completely different readability profile.

Formula summary table

Formula	Inputs	Best for
Flesch Reading Ease	Syllables, sentences	General content, gov. guidelines
Flesch-Kincaid Grade	Syllables, sentences	US education context
Gunning Fog	Polysyllables, sentences	Business/journalism
SMOG	Polysyllables, sentences	Health communications
Coleman-Liau	Letter counts, sentences	Automated/NLP pipelines
ARI	Character counts, sentences	Fast automated scoring
Dale-Chall	Known-word list	Educational material
Linsear Write	Syllable weighting	Technical manuals

Practical targets

Most plain-English style guides recommend targeting Flesch Reading Ease ≥ 60 (8th-grade level) for public-facing web content, emails, and user documentation. Medical guidelines and financial disclosures often target Flesch 50-60. Academic and legal text typically falls in the 0-30 range — which is appropriate for that audience but inappropriate for consumer communications.