What readability formulas actually measure
Every mainstream readability formula reduces to two ingredients: how long your sentences are, and how long (or complex) your words are. Flesch, Flesch–Kincaid, Gunning Fog, SMOG, Coleman–Liau and ARI each mix those ingredients differently, which is why the same passage gets six different verdicts. Understanding the recipe tells you exactly which edits will move a stubborn score.
The six formulas, decoded
- Flesch Reading Ease weighs syllables per word and words per sentence, and outputs 0–100 where higher means easier. It punishes polysyllabic vocabulary hardest.
- Flesch–Kincaid Grade uses the same inputs but restates them as a US school grade — handy for setting concrete targets.
- Gunning Fog counts the share of words with three or more syllables. Jargon-dense business writing gets savaged here even when sentences are short.
- SMOG also counts polysyllables but samples sentences differently; it was designed for health materials, where misreading has real consequences, and tends to score slightly stricter.
- Coleman–Liau ignores syllables entirely and uses characters per word — which makes it the only classic formula unaffected by how you'd pronounce a term.
- ARI likewise runs on characters and sentence length, so acronym-heavy technical text scores differently here than under Fog.
Why the scores disagree — and which to trust
A passage full of short technical acronyms ("API", "SQL") looks easy to syllable-counting formulas and hard to character-counting ones. A passage of long, flowing but simple sentences does the opposite. The practical answer: don't chase one number. When all six agree you're writing at graduate level, simplify; when they split, look at which kind of complexity each is flagging — long sentences or heavy words — and fix that specifically.
Edits that actually move the score
- Split compound sentences. One idea per sentence is the single highest-leverage edit; every formula rewards it.
- Swap Latinate words for Anglo-Saxon ones. "Use" beats "utilise", "help" beats "facilitate", "end" beats "terminate". This directly attacks the polysyllable counts in Flesch, Fog and SMOG.
- Cut throat-clearing. Openers like "It is important to note that" add words without meaning and drag sentence length up.
- Prefer active voice. Passive constructions run longer and bury the actor.
- Break up noun stacks. "Customer retention improvement strategy meeting" forces re-reading even though each word is common.
Paste your draft into the ToolCrix Word Counter, make one class of edit at a time, and watch which score responds — it's the fastest way to build an instinct for what your writing habitually gets wrong.
When to ignore the number
Readability formulas can't detect clarity — only surface complexity. A legally required disclosure, a scientific method section, or an audience of specialists may legitimately score "hard" while being perfectly clear to its readers. Conversely, short choppy nonsense scores beautifully. Treat the score as a smoke alarm, not a judge: it tells you where to look, and your own read-aloud test tells you whether there's a fire.
Sensible targets by audience
- General public / marketing — grade 7–9; most people skim.
- Health, finance, legal summaries — grade 6–8; comprehension under stress matters.
- Developer docs — sentence simplicity matters more than vocabulary; your readers know the jargon.
- Academic work — follow the field's conventions; the formula is irrelevant.
Frequently Asked Questions
Why does my text score differently in different tools?
Syllable counting is heuristic, and tools disagree on edge cases like hyphenated words and numerals — small input differences shift the output. Compare drafts within one tool, not scores across tools.
Which formula should I optimise for?
Flesch–Kincaid Grade is the most widely understood target. But the winning strategy is fixing whatever the formulas jointly flag: long sentences first, heavy vocabulary second.
Does readability affect SEO?
Not as a direct ranking input — but text people can actually read earns longer visits and more links, which do matter.
Check a draft now: run it through the Word Counter, or browse more guides.