How this readability checker works
- Paste your text. A few paragraphs give steadier scores than a single sentence.
- Read the band first. The overall band averages five grade-level formulas and shows how far apart they land.
- Use the details. The longest sentences and the hard words show where to simplify.
The checker splits your text into sentences and words, estimates syllables with the same engine as the syllable counter, and plugs the counts into six published formulas. It does not use AI and does not try to detect passive voice. Everything runs in your browser.
The formulas in plain language
All six use some of the same ingredients: how long your sentences are, how long your words are, or both. Here is what each one looks at. The formulas follow their published definitions, such as those described for Flesch Reading Ease and Flesch-Kincaid and SMOG.
Flesch Reading Ease
206.835 − 1.015 × (words ÷ sentences) − 84.6 × (syllables ÷ words)
A higher score means easier text. Long sentences and long words pull it down. As commonly published, 90 to 100 is very easy, 60 to 70 is plain English, 30 to 50 is difficult and under 30 is very difficult.
Flesch-Kincaid Grade Level
0.39 × (words ÷ sentences) + 11.8 × (syllables ÷ words) − 15.59
The same two ingredients as Reading Ease, weighted to give a US school grade.
Gunning Fog
0.4 × [(words ÷ sentences) + 100 × (complex words ÷ words)]
Complex words have three or more syllables. This checker leaves out capitalized words in the middle of a sentence, which are usually names.
SMOG
1.043 × √(words of three or more syllables × 30 ÷ sentences) + 3.1291
SMOG counts only the long words and was designed for samples of 30 sentences, so it is least reliable on short texts.
Coleman-Liau
0.0588 × (letters per 100 words) − 0.296 × (sentences per 100 words) − 15.8
This one counts letters instead of syllables, which makes it easy to compute reliably.
Automated Readability Index
4.71 × (letters ÷ words) + 0.5 × (words ÷ sentences) − 21.43
Also based on letters, plus average sentence length.
Why results vary a little between tools
Two tools can give slightly different scores for the same text. Deciding where a sentence ends (think “Dr. Smith” or “e.g.”) and how many syllables a word has both involve judgment calls, and the formulas are sensitive to them. That is why this page shows an overall band and the spread across formulas, and why a gap of a point or two between tools does not mean one is wrong.
What the scores cannot tell you
Readability formulas measure the surface of a text: how long the sentences are and how long the words are. They cannot tell whether your ideas are clear, whether your structure helps the reader or whether a technical term is one your audience already knows. A short sentence full of jargon can score as easy and still be hard to follow. Use the scores to spot long sentences and heavy words, and use your own judgment, or a reader, for everything else.
Using the results
Treat the numbers as a prompt to look at your writing, not a verdict. If the band is higher than you want, start with the longest sentences listed on the page and split them. Then look at the hard words and ask whether a plainer word would do the same job. If the band is lower than you want, make sure you are not talking down to readers. For long documents, check how many pages they fill with the words-to-pages converter, and how long they take to read with the reading time calculator.