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 maps text to a 0-100 scale where 100 is "trivially easy to read" and 0 is "impossible." The formula is 206.835 - 1.015 × (words/sentences) - 84.6 × (syllables/words). Most newspapers target 60-70 (plain English, grade 8-9 reading level). Academic writing typically lands in 30-50. Legal documents and technical specs frequently score below 30. Flesch-Kincaid Grade is the same input with different coefficients, output as a US school grade — grade 8 is mainstream newspaper writing, grade 12 is The Economist, grade 16+ is academic journal prose.

Gunning-Fog, SMOG, and Coleman-Liau

Gunning-Fog (1952) counts "complex words" (3+ syllables, excluding common suffixes) instead of total syllables. It tends to be slightly stricter than Flesch-Kincaid for the same text. SMOG (Simple Measure of Gobbledygook, 1969) was designed by McLaughlin specifically for health-literacy contexts and is the standard used in medical patient-education writing — the US National Library of Medicine recommends SMOG grade 6-8 for patient materials. Coleman-Liau (1975) cleverly avoids syllable counting entirely — it uses average characters per word and average words per sentence — which makes it more reliable on text with unusual vocabulary that syllable-counters mishandle. The five formulas usually agree within a grade or two; if they disagree wildly, one or two are likely being thrown off by an edge case (lots of acronyms, very short text, unusual capitalisation).

Writing for ASEAN ESL audiences

One regional consideration. Singapore, Malaysia, and the Philippines have high English literacy, but a significant share of readers are ESL (English as a Second Language) — they read English fluently for work but find dense native-speaker prose harder than a US/UK native would. A useful rule of thumb when writing for ASEAN business audiences: aim for Flesch-Kincaid grade 8-9 (one or two grades below the US business-press default). Indonesian and Vietnamese-language readers' English-text readability falls another grade or two below that. Marketing copy, product descriptions, and HR communications across the region read more smoothly when written to a deliberately lower grade level than the writer's instinct would produce.

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. Hemingway scores Flesch-Kincaid grade 4. 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.