Readability Score Calculator - Flesch, Flesch-Kincaid, Gunning Fog, SMOG

Every formula uses the same few counts. Flesch Reading Ease = 206.835 - 1.015 x (words / sentences) - 84.6 x (syllables / words); higher means easier (Flesch, 1948). Flesch-Kincaid Grade Level = 0.39 x (words / sentences) + 11.8 x (syllables / words) - 15.59, a US school grade (Kincaid and others, 1975). Gunning Fog = 0.4 x ((words / sentences) + 100 x (complex words / words)), where complex words have three or more syllables (Gunning, 1952). Automated Readability Index = 4.71 x (characters / words) + 0.5 x (words / sentences) - 21.43 (Senter and Smith, 1967).

Coleman-Liau = 0.0588 x L - 0.296 x 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). SMOG = 1.0430 x sqrt(polysyllables x 30 / sentences) + 3.1291, where polysyllables are words of three or more syllables (McLaughlin, 1969). SMOG was built on a sample of 30 sentences, so with fewer the tool shows Not enough sentences instead of a number. With more, it uses all the sentences and scales the count to 30; McLaughlin's own hand method took ten sentences each from the start, middle and end.

Sentences end at a full stop, exclamation mark, question mark or ellipsis that is followed by a space and then something other than a lower-case letter, and at a blank line (or at every line break if you switch that on). A full stop after Dr., Mr., Mrs., Prof., St., etc.-style abbreviations, a single capital initial (J. K. Rowling) or a dotted abbreviation (U.S., e.g., a.m.) does not end a sentence, and neither does the point in a number such as 3.14. Colons and semicolons never end one, although Flesch's original rules counted them. A numbered or bulleted line counts as a sentence of its own and its marker is not a word. The price of the abbreviation rule is that a sentence which really does end in one, such as in the U.S. or at 5 p.m., runs on into the next. Different tools make different choices here, which is one reason scores differ between sites.

Syllables are estimated by rule, not looked up, and the page says so. The counter counts groups of vowels, drops silent endings (-e, -ed, -es), adds a syllable for pairs such as ia, io and ua when they are sounded separately, and uses a short list of exceptions such as Mr, business and people. A figure such as 2026 counts as one syllable, as Flesch's rules say; a switch under the text counts one per digit instead. A hyphenated word is counted in parts. It only knows English spelling. Checked on 13 October 2026 against the CMU Pronouncing Dictionary, on the 98% of running words in three public-domain novels (Frankenstein, Dracula and The Time Machine, 264,010 words) that the dictionary lists, it matched at least one listed pronunciation for 99.6% of words and the first listed one for 99.0%. On Pride and Prejudice and on Alice's Adventures in Wonderland it matched 99.6% and 99.8%. The misses were almost all a single syllable out. Against the first listed pronunciation it counted 0.2 to 0.5 syllables too few per 100 words, which raises Flesch Reading Ease by about 0.2 to 0.4 points and lowers grade levels by about 0.02 to 0.05. Plain novels are an easy test: across all 117,493 dictionary entries made only of letters, which include rare words and names, it matched 93.2%.

How to read the scores. A Flesch Reading Ease of 60 to 70 is plain English, 30 to 50 is difficult, and the score can fall below 0 or rise above 100 for extreme text. The grade formulas give a US school grade, so 8 means roughly a 13 or 14 year old. They are most useful for comparing two drafts of the same piece, not for a verdict on one. They measure sentence and word length only: they cannot tell whether the text is clear, correct or well organised. They are calibrated on English prose and do not apply to Sinhala or Tamil; the tool warns when a large part of the text is not in the Latin alphabet.