How the Flesch reading ease score works
Rudolf Flesch published the reading ease formula in 1948, and J. Peter Kincaid adapted it into a US school grade level for the US Navy in 1975. Both rely on two things: sentence length and word length (in syllables). Long sentences and long words make text harder to read.
What the score means
| Score | Difficulty | Typical reader |
|---|---|---|
| 90–100 | Very easy | Age 10–11 |
| 80–89 | Easy | Conversational English |
| 70–79 | Fairly easy | Age 12–13 |
| 60–69 | Plain English | Age 13–15; good target for the web |
| 50–59 | Fairly difficult | Age 15–18 |
| 30–49 | Difficult | College |
| 0–29 | Very difficult | Graduate; academic and legal text |
The other indexes
- Gunning fog: years of education needed to understand the text on first reading, based on sentence length and the share of words with three or more syllables.
- SMOG: widely used for health information; it estimates the grade needed for full understanding. It's most reliable on 30 sentences or more.
- Coleman-Liau and Automated Readability Index: count letters instead of syllables, so they're quick for computers but less precise for short texts.
The scores often disagree by a grade or two, because each uses a different formula. Look at the overall picture, not a single number. Syllables are counted by a rule-based estimate, so scores can differ slightly from other tools.
How to make writing easier to read
- Shorten sentences. Aim for an average of 15–20 words. Split anything over 25, usually at "and", "but", "which" or a semicolon.
- Use everyday words: "use" not "utilise", "help" not "facilitate", "start" not "commence", "about" not "approximately".
- Write in the active voice: "We fixed the bug" is shorter and clearer than "The bug was fixed by us".
- One idea per sentence and one topic per paragraph.
- Use lists and headings so readers can scan.
- Cut filler: "in order to" → "to", "due to the fact that" → "because".
The sample text shows the difference: on its own, the first paragraph scores about 68 (plain English) and the second scores below zero (very difficult), though they say the same thing.
When a low score is fine
Readability formulas measure surface features, not meaning. Technical, legal or academic writing for expert readers can score low and still be clear to them. And short words don't guarantee clarity: a text can score well and still be confusing. Use the score as a guide, and read your text aloud as a final check. Count words with the word counter, or compare two drafts with text compare.
Frequently asked questions
What is a good Flesch reading ease score?
60 or above is plain English that most adults read easily. Aim for 60–70 for websites and general audiences.
What is the Flesch-Kincaid grade level?
An estimate of the US school grade needed to understand the text. Grade 8 means an average 13–14-year-old could read it.
How do I improve my readability score?
Use shorter sentences and shorter, everyday words. Splitting sentences over 25 words has the biggest effect.
Why do readability tools give different scores?
They use different formulas and count syllables in slightly different ways, so expect differences of a few points.
Does readability affect SEO?
Not directly as a ranking factor, but clear writing keeps readers on the page and helps them find answers, which search engines value.
Last updated October 2026 · More text tools