Readability Checker

What the readability checker measures

Readability formulas estimate how hard a text is to read from two things you can count: sentence length and word length. They say nothing about whether the text is true or well organized, but they flag the passages most likely to slow a reader down.

This checker counts words, sentences, syllables and letters in your text, then runs six published formulas on the same counts. The Flesch Reading Ease score and the Flesch-Kincaid grade level come first. Switch on all six to add the Gunning Fog Index, the SMOG grade, the Coleman-Liau Index and the Automated Readability Index. Open any formula to see it with your numbers filled in, and its source. For a quick count with reading time, the word counter shows the two Flesch scores too.

Flesch Reading Ease scores and grade levels

The Flesch Reading Ease score usually lands between 0 and 100. Higher means easier: Flesch described 0 as practically unreadable and 100 as extremely easy. He matched the scores to US school levels in his book How to Write Plain English:

Flesch set 60 as the minimum for plain English, about 20 words per sentence and 1.5 syllables per word, and asked for at least 80 in conversational writing for consumers. For comparison, he reported 65 for Reader's Digest, 52 for Time, 39 for the New York Times and minus 6 for the Internal Revenue Code. A grade level from the other formulas reads the same way: 8 means a US eighth grader should be able to follow the text, 13 to 16 are college years and 17 or more is graduate level, as Gunning and McLaughlin label their scales.

The six formulas and where they come from

• Flesch Reading Ease. Rudolf Flesch published it in 1948 in the Journal of Applied Psychology. It is the only score on this page where higher means easier.
• Flesch-Kincaid Grade Level. In 1975 J. Peter Kincaid and colleagues recalculated the Flesch formula for the US Navy as a direct grade level, testing 531 enlisted sailors on 18 passages from Navy training manuals (Research Branch Report 8-75).
• Gunning Fog Index. Robert Gunning, The Technique of Clear Writing (revised edition, 1968): 0.4 times the sum of the average sentence length and the percentage of hard words. Hard words have three or more syllables, but proper names, compounds of short words like bookkeeper and verbs that reach three syllables only through -ed or -es do not count. Gunning called 13 and up the danger line.
• SMOG Grade. G. Harry McLaughlin, Journal of Reading, 1969 (original paper). It counts words of three or more syllables in 30 sentences. The checker uses his regression equation, 3.1291 + 1.0430 × the square root of that count, and scales your text to 30 sentences. His quick version is 3 plus the square root.
• Coleman-Liau Index. Meri Coleman and T. L. Liau, Journal of Applied Psychology, 1975: 0.0588 × letters per 100 words − 0.296 × sentences per 100 words − 15.8. It counts letters instead of syllables, which a computer can do exactly.
• Automated Readability Index. E. A. Smith and R. J. Senter, 1967, in a report for the Aerospace Medical Research Laboratories: 4.71 × characters per word + 0.5 × words per sentence − 21.43. It was made to be counted by a counter on the typewriter while the text was typed, and was later checked on Air Force technical manuals.

Why the grade levels disagree

Each formula was fitted to a different test of understanding. Kincaid's team graded a Navy passage at the level where half the readers of that grade filled in at least 35% of the blanks in a cloze test, where readers supply words left out of the passage. Gunning matched his index to school passages that students of a grade could answer nine of ten questions about. McLaughlin took the grade of readers who answered every question, a stricter standard, and noted that SMOG grades usually come out about two grades above Dale-Chall levels. So a spread of two or three grades between formulas is normal. The Navy report itself says readability formulas are only accurate to within about one grade level.

How syllables, words and sentences are counted

The syllable count is an estimate. The checker uses English spelling rules (silent e, -ed after most letters, vowel pairs like the ia in media) plus a list of common words the rules get wrong. Where a dictionary gives two pronunciations, it follows Flesch's rule to use the one with fewer syllables, so every and family count two. We tested it against the Carnegie Mellon University Pronouncing Dictionary. On 8,229 common words from a list of the 10,000 most frequent English words it matched one of the dictionary pronunciations for 99.1% and was off by more than one syllable for under 0.1%. We tuned the rules on that list, so the fairer number is 96.1% on 26,457 rarer dictionary words.

• Words: contractions, hyphenated words, numbers, abbreviations and web addresses count as one word each, as Flesch's counting rules say.
• Syllables: numbers, abbreviations like USA and symbols count as one syllable, also following Flesch.
• Sentences: a sentence ends at a period, question mark or exclamation point, or at a line break. Periods after Mr., Dr., e.g. and similar abbreviations do not end a sentence. Flesch's rules test only running text, so you can skip headings and list lines without an end mark.
• Characters: the Automated Readability Index counts every character except spaces, as the typewriter counter did. Coleman-Liau counts letters and digits only.

How to make text easier to read

The tips next to your text are general writing advice, built from the counts. A few that work for most texts:

• Split long sentences where a new idea starts, often at and, but, which or because.
• Swap long words for short ones where the short word means the same: use instead of utilize, about instead of approximately, help instead of facilitate. Find and replace swaps a word everywhere at once, and the word frequency counter shows which words you use most.
• Keep the words your readers need. A technical term your audience knows is clearer than a vague short word. Explain it once if some readers might not know it.
• Read it aloud. The formulas cannot hear rhythm or notice a missing step; text to speech reads your text back to you. Stock phrases are worth a look too; the AI phrase finder highlights the ones chatbots overuse.

How to use the readability checker

1. 1Paste your text into the box, or press Example to try a sample. The Flesch Reading Ease score, the Flesch-Kincaid grade level and the counts update as you type.
2. 2Press Show all six formulas for more grade levels, and open any formula to see the math with your numbers and its source.
3. 3Set what counts as a long sentence, check the highlighted text and the tips, rewrite, and paste again. Copy report gives you the scores as plain text.

Built by Tobias Kurth, designer. Updated October 13, 2026.

Frequently asked questions