What the Flesch Reading Ease Score Actually Measures

The formula is older than you'd think

The Flesch Reading Ease formula was published by Rudolf Flesch in 1948, and it's still the most widely used readability metric today — it's built into Microsoft Word's own readability statistics, and U.S. government agencies and the insurance industry have required documents to hit a minimum Flesch score for decades.

What it actually measures

The formula is 206.835 − 1.015 × (words ÷ sentences) − 84.6 × (syllables ÷ words). Notice what it does not look at: it has no idea whether your vocabulary is technical, whether your argument is logically sound, or whether your sentence structure is clear. It only measures two proxies for difficulty — how long your sentences run, and how many syllables your words carry — and treats both as stand-ins for reading effort. That's a deliberately narrow, mechanical measurement, not a judgment of writing quality.

Reading the score

Higher scores mean easier reading: 90–100 is "Very Easy" (roughly a 5th-grade level, like a children's book), 60–70 is "Standard" (comparable to a typical newspaper or magazine article), and anything under 30 is "Very Confusing" (dense academic or legal writing). Most general-audience web content aims for 60–70; plain-language guidelines for government and healthcare writing often target 80 or higher.

Where the formula breaks down

Because it only counts sentence length and syllables, Flesch can be fooled in both directions. A string of short, choppy sentences using obscure jargon can still score "easy" if the words happen to be short (syllable count is a poor proxy for familiarity — "iPad" and "the" both count as one syllable). Conversely, one long but perfectly clear sentence can drag a score down even if every reader follows it without trouble. Treat the number as a rough signal to revisit your draft, not a precise verdict on how understandable it is.

Try it yourself

Our Readability Score Calculator computes both the Flesch Reading Ease score and the related Flesch-Kincaid Grade Level instantly as you type or paste text, with the underlying word, sentence and syllable counts shown alongside.