Readability Scorer — Flesch-Kincaid, Gunning Fog & SMOG Index
Analyze your text with five readability formulas at once: Flesch-Kincaid, Gunning Fog, SMOG, ARI, and Coleman-Liau. Get a consensus reading grade level, word stats, and highlighted long sentences instantly.
How this readability scorer computes six readability scores from one syllable counter
Readability formulas all reduce to the same two ingredients: how long your sentences are and how long your words are, expressed as syllables. The formulas themselves are simple linear equations published decades ago. The genuinely hard part, the part no formula's paper actually solves, is counting syllables in code without a dictionary. This tool uses a rule based syllable counter, checked against a pronunciation dictionary, and feeds the counts into six classic readability equations at once.
Every calculation happens in your browser as you type or click analyze. No text is transmitted anywhere.
How syllables are counted
This is the piece that makes or breaks every score below it, so it is worth reading closely.
well-known is counted as well plus known.
people, recipe, business and everyone, returns a fixed count.
-ology, -fully, -ment, -ness, over- and un- are counted with their known syllable value and removed.
e or -ed after most consonants, take one off. Patterns that sound as two, like -ia in media or -ism, add one.
The rules are adapted from the open source syllable package. We checked them against the CMU Pronouncing Dictionary on a few thousand words of real web copy: they agree on about 99 percent of word uses, where the simple vowel group rule this page used before agreed on about 94 percent. Words in other languages are not handled, so the scores are meant for English.
Flesch Reading Ease and Flesch-Kincaid Grade Level
Rudolf Flesch published the Reading Ease formula in 1948 in his paper A New Readability Yardstick. The Flesch-Kincaid Grade Level variant was developed later, in 1975, for the United States Navy to grade technical manuals. Both use the same two inputs, average sentence length in words and average syllables per word, with different weights.
| Ease score | Reading level |
|---|---|
| 90 to 100 | Very easy, 5th grade |
| 70 to 89 | Easy to fairly easy, 6th to 7th grade |
| 60 to 69 | Standard, 8th to 9th grade |
| 30 to 59 | Fairly difficult to difficult, high school to college |
| Below 30 | Very difficult, graduate and professional level |
Three more formulas, computed alongside
Gunning Fog Index
Robert Gunning published this in 1952. It weighs complex words alongside sentence length. Following Gunning's rules, a complex word has three or more syllables but is not a proper noun, not a hyphenated compound, and not a word that only reaches three syllables through an -es, -ed or -ing ending: 0.4 * (asl + 100 * complexWords / words). It was built for business writing, so it leans harder on penalizing long, jargon heavy words.
SMOG Index
G. Harry McLaughlin's 1969 formula, 1.0430 * sqrt(polysyllables * (30 / sentences)) + 3.1291, where polysyllables are all words of three or more syllables. It needs at least three sentences in this tool and is left out of the average below that, since scaling a very short passage up to a 30 sentence sample is unstable.
Automated Readability Index
Developed for the US Air Force in 1967, and unlike the others it uses characters per word instead of syllables per word: 4.71 * (chars/words) + 0.5 * (words/sentences) - 21.43, where chars are letters and digits only, so punctuation does not inflate the score. Character counting sidesteps the syllable heuristic entirely for this one metric.
Coleman-Liau Index
Published in 1975 by Meri Coleman and T.L. Liau, also character based: 0.0588L - 0.296S - 15.8, where L is letters per 100 words and S is sentences per 100 words. It was designed to be easy to compute by a typewriter operator counting letters, no syllable estimation required.
The tool averages the five grade level outputs, Flesch-Kincaid Grade, Gunning Fog, SMOG, ARI and Coleman-Liau, into a single consensus grade level, rounded to one decimal. Grades below zero count as zero, and SMOG is skipped when the text has fewer than three sentences, so no single formula's blind spot dominates the headline number.
A worked readability score
Input: "The cat sat on the mat. It was a sunny day." Result: 11 words, 2 sentences and 12 syllables give a Flesch Reading Ease of 109.0. The formula can go above 100 on very short simple sentences and the tool shows the real value, labeled Very Easy. The Flesch-Kincaid Grade Level works out to minus 0.6 and is shown as 0.
Reading time is estimated separately as words / 238 minutes, shown in minutes and seconds, where 238 words per minute reflects published averages for adult silent reading speed in English.
- Flesch-Kincaid readability tests covers the history and exact coefficients of both formulas.
- Gunning fog index for Robert Gunning's original 1952 method.
- SMOG grading for McLaughlin's 1969 paper and its 30 sentence sampling design.
- Automated Readability Index for the character based US Air Force formula.
- Coleman-Liau Index for the 1975 letters and sentences per 100 words method.
Who needs a readability score
Checking a blog draft against an 8th grade reading level target before publishing, scoring patient facing medical instructions where plain language rules apply, grading a legal disclaimer for a general audience, testing whether onboarding copy in an app is simple enough for new users, and comparing two versions of the same paragraph to see which one actually reads easier rather than just guessing.
FAQ: Readability Scorer
For general web content, aim for a Flesch Reading Ease score between 60 and 70, which corresponds to a grade level of 7 to 9. This is readable by most adults without feeling oversimplified. Marketing copy and landing pages often target 70 to 80. Academic or technical writing may sit below 50.
The Flesch-Kincaid test produces two scores. The Reading Ease score usually runs from 0 to 100, and higher means easier to read. The Grade Level score maps the text to a U.S. school grade, so a score of 8 means an 8th-grader could understand it. Both use average sentence length and average syllables per word as inputs.
The Gunning Fog Index estimates the years of formal education needed to understand a piece of writing on a first read. It weighs average sentence length and the percentage of complex words, those with three or more syllables. A score of 12 corresponds to a high school senior. Most popular publications target a Fog score below 12.
SMOG (Simple Measure of Gobbledygook) focuses on polysyllabic words, those with three or more syllables, counted per 30 sentences. It was designed for health communication and tends to produce slightly higher grade estimates than Flesch-Kincaid. It is considered more accurate for texts above a 6th-grade level.
The two fastest wins are shorter sentences and simpler words. Break any sentence over 20 words in two. Replace multi-syllable words with shorter synonyms where meaning is not lost. Use active voice. Avoid jargon unless your audience demands it. After editing, paste your text back into this readability scorer to measure the improvement.
Yes. The readability scorer is completely free with no word limits and no account required. All calculations run in your browser so your content stays private.
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