Paste your text and all four readability scores calculate instantly, together with the word, sentence and syllable counts they are built from and a plain-English reading of what each score means.
Scores run from 0 to 100, where 60 to 70 is plain English suitable for most adults and newspapers, 30 to 50 is difficult and typical of academic writing, and below 30 is very hard. Higher is easier, which is the opposite direction to the grade-level scores.
Look at them together. Flesch-Kincaid, Gunning Fog and SMOG all report a US school grade level, and if all three cluster around the same number that is a solid signal, while a wide spread usually means unusual sentence lengths or lots of long technical terms.
Syllables are estimated with a vowel-group heuristic that merges consecutive vowels, drops silent trailing e, and handles the -le ending and common exceptions. It is very close to a dictionary count for ordinary English but can be off by one on unusual names and loanwords.