Readability calculator

What a readability score measures

A readability formula turns two things you can count, how long the sentences are and how long the words are, into a number that predicts how hard a text is for a reader. Rudolf Flesch published the first widely used one in 1948; the US Navy researchers J. P. Kincaid and colleagues re-fitted it in 1975 so that it gave a US school grade instead of an index. The formulas never read the text for meaning. They count, so they are fast and repeatable, and they are also blind to everything that is not length: a short sentence full of jargon scores as easy.

Paste your text above and the tool counts words, sentences, syllables and letters, then applies six published formulas. The headline number is the Flesch–Kincaid grade level, where 8.0 means roughly the reading level of a US eighth grader. Flesch Reading Ease runs the other way: higher is easier, and the table below the result names the band.

The six formulas and their variables

Flesch Reading Ease = 206.835 − 1.015 × (words ÷ sentences) − 84.6 × (syllables ÷ words). The scale used with it runs from 90–100 (very easy, 5th grade) down through plain English around 60–70 to under 10 (extremely difficult, professional level).

Flesch–Kincaid Grade Level = 0.39 × (words ÷ sentences) + 11.8 × (syllables ÷ words) − 15.59. It uses the same two ratios as Reading Ease, so the two always move together.

Gunning Fog = 0.4 × [(words ÷ sentences) + 100 × (complex words ÷ words)]. Robert Gunning, in The Technique of Clear Writing (1952), counted a word as complex when it has three or more syllables, leaving out proper nouns, familiar jargon, compound words, and words that reach three syllables only through -es, -ed or -ing. This tool applies the same exclusions with simple rules: a capitalized word that is not the first word of its sentence is treated as a proper noun, a hyphenated word is judged part by part, and -ing, -ed and -es endings are not counted as the third syllable.

SMOG = 1.0430 × √(polysyllables × 30 ÷ sentences) + 3.1291, from G. Harry McLaughlin (Journal of Reading, 1969). Polysyllables are all words with three or more syllables. The formula was normed on 30 sentences, so with fewer sentences the tool scales the count to 30, which makes it less dependable on a short paragraph.

Coleman–Liau = 0.0588 × L − 0.296 × S − 15.8, where L is the average number of letters per 100 words and S the average number of sentences per 100 words (Coleman and Liau, 1975). It needs no syllable count at all, which makes it the formula least affected by the guessing in this tool. The Automated Readability Index = 4.71 × (characters ÷ words) + 0.5 × (words ÷ sentences) − 21.43 (Smith and Senter, 1967) also counts letters, and its result is rounded up to the next whole grade.

A worked example

Take the sentence used to illustrate the Flesch formulas on Wikipedia: "The Australian platypus is seemingly a hybrid of a mammal and reptilian creature." It has 13 words, 1 sentence and 24 syllables, so words per sentence is 13 and syllables per word is 24 ÷ 13 = 1.846. Reading Ease is 206.835 − 1.015 × 13 − 84.6 × 1.846 = 37.5, which is "difficult", and the grade level is 11.3.

Sentence length alone can move a score a long way. This calculator gives "The committee has determined that implementation of the aforementioned methodology should be postponed until additional documentation becomes available." a grade level of 22.2 and Reading Ease -32.3. Rewritten as "The committee decided to wait. It wants more paperwork first." the same message scores grade 5.2 and Reading Ease 66.4. For comparison, the abstract of the 1975 Coleman–Liau paper has 5 sentences, 119 words and 639 letters and digits, which the Coleman–Liau formula turns into grade 14.5.

How this calculator counts

A word is a run of letters or digits with apostrophes and hyphens inside it; "well-known" and "it's" are one word each, and a number such as 1,200 counts as one word of one syllable. A sentence ends at a period, question mark or exclamation mark followed by a space or the end of the text. Abbreviations such as Mr., Dr., e.g. and initials do not end a sentence, and an ellipsis before a lowercase letter does not either. A heading with no full stop runs into the line below it, and colons and semicolons do not end sentences; add a period to headings and bullet items, or the sentence count will be too low and every score too high.

Syllables are counted by a set of spelling rules (vowel groups, silent final e, -ed and -es endings, a few common patterns and a short list of exceptions), not by a pronunciation dictionary. Checked against dictionary syllable counts on lists of everyday words that the rules had not been fitted to, it got roughly 93 to 97 words in 100 exactly right, and almost every miss was one syllable off. It is weakest on names, loanwords and abbreviations. Because the error is small per word and tends to cancel out, grade levels from a text of a few hundred words are normally within a fraction of a grade of a dictionary-based count; for a few sentences, a single miscounted word can move the result noticeably.

Limits of readability formulas

They are weak proxies for comprehension. Crossley, Allen and McNamara (2011, Reading in a Foreign Language) note that traditional formulas rely only on sentence length and word length, have been widely criticized as weak indicators of comprehensibility, and ignore reader characteristics and text features such as syntactic complexity, rhetorical organization and the density of ideas. A paragraph of short words in a confusing order can score as easy; a clear explanation with a few necessary technical terms can score as hard. Use the number to spot long sentences and heavy words, not to certify that a text is understandable.

They depend on the sample. Gunning advised testing a passage of about 100 words without skipping sentences, and SMOG was fitted to 30 sentences; scores from a single short paragraph can swing by several grades. They also say nothing about layout, headings or examples, and the grade they report is a US school grade for native English readers: it does not tell you how a second-language reader or a reader with a specific condition will fare. Finally, the formulas can be gamed: chopping every sentence in half lowers the score without making the text clearer.

What is a good Flesch Reading Ease score?

Higher means easier. On the scale published with the Flesch formula, 90–100 is very easy (5th grade), 80–90 easy (6th grade), 70–80 fairly easy (7th grade), 60–70 plain English (8th–9th grade), 50–60 fairly difficult (10th–12th grade), 30–50 difficult (college), 10–30 very difficult (college graduate) and below 10 extremely difficult (professional). There is no single right target: a children's story and a legal contract should land in different places. If a general audience should follow the text without effort, scores in the 60s and 70s are the usual aim.

Why do the six formulas give different grades?

Each was fitted to different readers and different tests. Flesch–Kincaid and Reading Ease use syllables, Coleman–Liau and ARI use letters, Gunning Fog and SMOG count long words. SMOG looks only at words of three or more syllables and is scaled to 30 sentences, so a short text with a few long words can push it well away from the others. A spread of a grade or two is normal; if one formula is far from the others, check for a very long sentence, a list or a passage full of names and numbers.

How many words do I need for a reliable score?

Gunning suggested a sample of about 100 words with no sentences skipped, and SMOG expects 30 sentences. Below roughly 100 words the tool warns you, because one long sentence or one technical term can move the result by several grades. For a long document, paste a few separate passages from the beginning, middle and end and compare them rather than relying on one number.

Does it work for other languages?

No. The constants in these formulas were fitted to English texts and English syllable patterns, and the syllable rules in this tool are for English spelling. Other languages have their own adapted formulas; the English numbers would mislead there.

What grade level should I write at?

It depends on the readers and the purpose, and the formulas cannot decide that for you. Use them to compare drafts: if a revision lowers the grade level while keeping the same content, you have probably shortened sentences or swapped long words for shorter ones. For a quick check on length alone, see the word count calculator; to estimate how long the text takes to read aloud or silently, use the reading time calculator.

Is the text I paste stored or sent anywhere?

No. The counting runs in your browser. The page keeps your last text in your own browser storage so that it is there when you return, and nothing is uploaded.

Sources, checked October 27, 2026: R. Flesch, "A new readability yardstick", Journal of Applied Psychology 32(3), 1948, 221–233; J. P. Kincaid, R. P. Fishburne, R. L. Rogers and B. S. Chissom, Derivation of new readability formulas for Navy enlisted personnel, Research Branch Report 8-75, Naval Technical Training, 1975; R. Gunning, The Technique of Clear Writing, McGraw-Hill, 1952; G. H. McLaughlin, "SMOG grading — a new readability formula", Journal of Reading 12(8), 1969, 639–646; M. Coleman and T. L. Liau, Journal of Applied Psychology 60, 1975, 283–284; E. A. Smith and R. J. Senter, Automated Readability Index, AMRL-TR-6620, 1967; S. A. Crossley, D. B. Allen and D. S. McNamara, "Text readability and intuitive simplification: a comparison of readability formulas", Reading in a Foreign Language 23(1), 2011, 84–101. Related: the word count calculator, reading time calculator, average calculator and grade calculator. How we check our calculators.