Text Statistics & Readability

Readability formulas existed long before computers. The Flesch Reading Ease formula was published by Rudolf Flesch in 1948; the Flesch-Kincaid Grade formula was developed for the US Navy in 1975 to assess training manuals. The point of all of them is the same: turn a piece of writing into a number that approximates how hard it is to read. The five formulas this tool implements — Flesch, Flesch-Kincaid, Gunning-Fog, SMOG, and Coleman-Liau — all rely on the same two intuitions: shorter sentences are easier than longer ones, and shorter words (fewer syllables) are easier than longer ones. They differ in the specific weighting and in whether they output a "grade level" (years of education) or an "ease score" (0-100).

Flesch Reading Ease and Flesch-Kincaid Grade

Flesch Reading Ease gives a score where higher is easier. The formula is 206.835 - 1.015 × (words/sentences) - 84.6 × (syllables/words), and very short or very long sentences can push it past 100 or below 0; the page prints it as computed. The band names beside it (very easy to very difficult) are the conventional reading of the scale, usually attributed to Flesch's 1948 paper, which we have not been able to check. Microsoft's help for Word suggests a score "between 60 and 70" for most standard files. Flesch-Kincaid Grade takes the same two inputs with Kincaid's 1975 coefficients, 0.39 × (words/sentences) + 11.8 × (syllables/words) - 15.59, and reports a US school grade; Microsoft suggests "around 7.0 to 8.0" for most documents.

Gunning-Fog, SMOG, and Coleman-Liau

Gunning-Fog (1952) counts words of three or more syllables, leaving out capitalised names and words that reach three syllables only through -ed, -es or -ing. SMOG (Harry McLaughlin, 1969) counts every word of three or more syllables; McLaughlin fitted it to complete comprehension and normed it on 30-sentence samples, so on a shorter text the page marks it unreliable. Coleman-Liau (1975) counts letters per word instead of syllables. The formulas often disagree by several grades on one text, and not because one of them is broken: each was fitted to its own readers and standard, and each counts something different.

English only, including in Singapore and Malaysia

All five formulas were built for English. The page does not score text that reads as Malay or Indonesian, text mostly in another script such as Chinese or Tamil, or Latin-script text heavy with accents such as Vietnamese, because the number would be meaningless: a Malay translation of plain English bus directions scores Flesch-Kincaid grade 14.9 against 3.5 for the same English, almost entirely from longer words. In mixed English and Chinese text, the scores cover the English words and sentences only. The word, character and reading-time counts above work on any text.

The limits of readability formulas

All these formulas measure surface complexity, not meaning. A sentence can be syntactically simple and conceptually dense, or syntactically convoluted and easy to understand once you see the structure. Very short sentences score low whatever they say: Heideggerian philosophy translated into short declarative sentences would score grade 6 — and still be impenetrable to most readers. The formulas are useful as directional feedback while editing: if a draft scores grade 14 and you're targeting general readers, shorter sentences and simpler word choices will help. They are not a substitute for reading the draft aloud or having someone unfamiliar with the topic try it.