The five formulas measure the same two things differently
It’s easy to be overwhelmed by five scores, but they’re mostly variations on a theme — they all reward shorter sentences and simpler words, just weighted differently:
| Formula | Counts | Best for |
|---|---|---|
| Flesch Reading Ease | Syllables + sentence length | Quick 0–100 gut check (higher = easier) |
| Flesch–Kincaid Grade | Syllables + sentence length | US grade-level target |
| Gunning Fog | ”Complex” words + sentence length | Business / technical writing |
| SMOG | Polysyllable density | Health and safety content (conservative) |
| Coleman–Liau / ARI | Characters (not syllables) | Automated pipelines (no syllable guessing) |
When they disagree, trust the character-based scores (Coleman–Liau, ARI) for automated reliability and Flesch–Kincaid for the number most editors and style guides expect.
What “good” looks like by audience
- General web / news: 7th–8th grade (Flesch Reading Ease 60–70). This is where most successful blogs and marketing copy land.
- Email and landing pages: aim even lower — 6th grade keeps conversion-critical copy frictionless.
- Technical docs: 10th–12th grade is acceptable when the audience is specialists, but never let jargon inflate it needlessly.
The principle behind every target: write at or below your reader’s level. Writing up to impress almost always costs you comprehension.
Why syllable counting is a heuristic, not gospel
English pronunciation is famously irregular (“queue” is one syllable, “area” is three), so any syllable-based formula uses a vowel-group heuristic with patches for silent-e, -le endings, and common prefixes. On a single odd word it can be off by one; across a full passage those errors average out, which is exactly how the formulas were designed to be used. Don’t over-read a one-point swing — look at the trend after an edit, not the third decimal place.
A workflow that compounds
Analyze, fix the three longest sentences, then re-analyze. That single loop, repeated twice, does more for clarity than any amount of word-by-word tinkering — because long sentences are where readers actually lose the thread.