Flesch reading ease and grade level, explained honestly

Rudolf Flesch published his reading-ease formula in 1948 after studying why adult readers gave up on government pamphlets, and it has been built into Word, government style guides and every content tool since. It is useful, simple and widely misread. This guide explains what the numbers count, what a target should be, and the ways a good score can hide bad writing — with the readability checker to try it on your own text.

The formula and what it counts

Reading Ease = 206.835 − 1.015 × (words per sentence) − 84.6 × (syllables per word). That's the whole thing: two averages, weighted so that long sentences and long words push the score down. The constants were fitted so that typical texts land between 0 and 100. Syllables are counted by rule (vowel groups, with corrections for silent e), which is an approximation the formula's designers accepted — the same one tools use today.

Reading the scale

• 90–100 very easy — comics, children's books, a 5th-grade level.
• 70–80 easy to fairly easy — popular fiction, 7th grade.
• 60–70 plain English — newspapers, most websites, 8th–9th grade. The common target.
• 50–60 fairly difficult — quality press, 10th–12th grade.
• 30–50 difficult — academic writing, college level.
• 0–30 very difficult — legal and scientific text, graduate level.

Two benchmarks: Reader's Digest historically scored around 65; insurance policies and terms of service commonly score in the 20s and 30s, which is roughly what Flesch was complaining about.

Grade levels and Gunning Fog

Flesch-Kincaid Grade Level (1975, commissioned by the US Navy for training manuals) reweights the same two averages into a US school grade: 0.39 × words per sentence + 11.8 × syllables per word − 15.59. A score of 8 means an average 8th-grader could follow it. Gunning Fog (1952) counts "complex" words — three syllables or more — instead of average syllables: 0.4 × (words per sentence + 100 × complex words ÷ words). All three agree in direction and disagree by a grade or two on the same text, which is fine; they're rulers, not microscopes.

What to aim for, by audience

The UK government's style guidance asks for content the average 9-year-old could read, and US federal plain-language rules target roughly grade 8, because a large share of adults read below a 10th-grade level and everyone reads faster at a lower one — including experts, who have no wish to work harder than necessary. So: landing pages, support articles, product descriptions, patient information and public notices at grade 7–9 (ease 60–70+). Marketing email and social copy lower still. Professional and academic audiences tolerate grade 10–12 but rarely need it. The exceptions are texts whose precision needs the long words — contracts, standards, papers — where chasing a score damages meaning.

What the score can't tell you

The formula counts length, not sense. "The cat sat on the mat and the dog ran to the park and it was fun" scores very easy and says nothing; a tight technical paragraph scores difficult and is perfectly clear to its readers. It doesn't see jargon (short words can be opaque), ambiguity, missing logic, or passive constructions that hide who did what. Treat a score as a prompt: if it's high, check the text isn't vacuous; if it's low, look at the longest sentences and the three-syllable words and ask which ones earn their place. The summarizer finds the sentences that carry the argument; How many words is a page? covers length; the word counter the reading time.