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Flesch-Kincaid Grade Level Explained
How the most common readability formula works, how to calculate it by hand, and where it falls short in a classroom.
The Flesch-Kincaid formula
The Flesch-Kincaid grade level estimates the US school grade needed to read a text. It uses two numbers: the average words per sentence and the average syllables per word. Longer sentences and longer words give a higher grade.
Grade = 0.39 × (words ÷ sentences) + 11.8 × (syllables ÷ words) − 15.59
Reading Ease = 206.835 − 1.015 × (words ÷ sentences) − 84.6 × (syllables ÷ words)
Where the formulas come from
Rudolf Flesch published the Reading Ease formula in 1948 to help writers produce plainer English. In 1975, J. Peter Kincaid and his colleagues reworked it for the US Navy, which wanted training manuals matched to the reading level of its recruits. The result was a version that outputs a school grade, and it soon spread into schools, publishing and word processors.
Worked example by hand
Say a passage has 120 words, 8 sentences and 156 syllables.
- Words per sentence: 120 ÷ 8 = 15
- Syllables per word: 156 ÷ 120 = 1.3
- Grade: 0.39 × 15 + 11.8 × 1.3 − 15.59 = 5.85 + 15.34 − 15.59 = 5.6
- Reading Ease: 206.835 − 1.015 × 15 − 84.6 × 1.3 = 81.6
So the passage sits at about a Grade 5 to 6 level and reads as “easy” on the Reading Ease scale.
Flesch Reading Ease score chart
| Score | Difficulty | Approximate school level |
|---|---|---|
| 90 to 100 | Very easy | Grade 5 |
| 80 to 89 | Easy | Grade 6 |
| 70 to 79 | Fairly easy | Grade 7 |
| 60 to 69 | Plain English | Grades 8 and 9 |
| 50 to 59 | Fairly difficult | Grades 10 to 12 |
| 30 to 49 | Difficult | College |
| 0 to 29 | Very difficult | College graduate |
What the formula cannot tell you
Readability formulas count. They do not read. That leaves real gaps a teacher needs to fill.
- Vocabulary. Cat and gnu both have one syllable, but one is far less familiar.
- Background knowledge. A short-sentence passage about cricket rules can still baffle a child who has never seen the game.
- Ideas and structure. Irony, flashbacks and abstract themes raise difficulty without changing sentence length.
- Short or unusual text. Poems, lists and dialogue break the sentence count, and passages under 100 words give unstable scores.
Use the grade level as a first check, then read the text with your students in mind.
How to lower the grade level of a passage
- Split long sentences at and, but and which.
- Swap long words for everyday ones: use for utilize, help for assistance.
- Keep technical words the lesson is teaching, and explain them instead of replacing them.
- Check the score again after each round of edits.
Other readability formulas
The Automated Readability Index (ARI) and Coleman-Liau count letters instead of syllables, which makes them less sensitive to how syllables are counted. The Gunning Fog index and SMOG focus on words of three or more syllables. When two or three formulas agree within a grade, you can trust the estimate more.
Frequently asked questions
What does a Flesch-Kincaid grade level of 6 mean?
It means a typical US sixth grader should be able to read the text. The score is an estimate based only on sentence length and word length.
What is the difference between Flesch Reading Ease and Flesch-Kincaid grade level?
Both use the same two measures. Reading Ease gives a score from about 0 to 100, where higher is easier. The grade level converts the result into a US school grade, where lower is easier.
Who created the Flesch-Kincaid formula?
Rudolf Flesch published the Reading Ease formula in 1948. J. Peter Kincaid and colleagues adapted it into a grade-level formula in 1975 for the US Navy.
How can I lower the grade level of a passage?
Shorten long sentences, split sentences joined by several clauses, and replace long words with shorter everyday ones where the meaning stays the same.
Is Flesch-Kincaid the same as Lexile?
No. Lexile is a separate, proprietary measure. Flesch-Kincaid is an open formula you can calculate yourself.
More guides
- How to Calculate WCPM Step-by-step scoring for a timed fluency read, with error rules and grade-level norms.
- Running Record Accuracy Levels What independent, instructional and frustration levels mean, plus an error-rate conversion chart.
- Self-Correction Ratio Explained How to work out the SC ratio, what a good ratio looks like, and prompts that build self-monitoring.
- Average Reading Speed by Grade and Age Oral reading fluency norms for Grades 1 to 6 and adult reading speeds, in one place.