Flesch Reading Ease is the readability score you are most likely to meet. Microsoft Word reports it, and many writing tools show it next to a grade level. It is simple enough to calculate by hand, which also makes its limits easy to see. This guide explains how the formula works, what the score ranges mean, how sentence length and syllables move the number, and how it differs from the Flesch-Kincaid Grade Level.
The formula and its history come from the sources listed at the end. The examples were written for this guide and scored with our readability score checker. Advice on using the score is WriterFlowLab's editorial guidance.
What the Flesch Reading Ease score is
Rudolf Flesch, a writing consultant and advocate of plain English, published the formula in 1948 in the Journal of Applied Psychology, in a paper titled "A new readability yardstick". The score rates text on a scale that usually runs from 0 to 100. The higher the score, the easier the text is to read.
The formula
Reading Ease = 206.835 − (1.015 × ASL) − (84.6 × ASW)
- ASL (average sentence length) is the number of words divided by the number of sentences.
- ASW (average syllables per word) is the number of syllables divided by the number of words.
That is the whole formula. It starts from a fixed number and subtracts a penalty for long sentences and a larger penalty for long words. Nothing in it stops the result going above 100 or below 0, so very simple or very dense text can land outside the usual range.
Score ranges
A commonly used interpretation of the scale:
- 90 and above: very easy
- 80 to 89: easy
- 70 to 79: fairly easy
- 60 to 69: standard
- 50 to 59: fairly difficult
- 30 to 49: difficult
- Below 30: very difficult
For reference, Microsoft's Word documentation says that for most standard files you want a score between 60 and 70. What is right for your text depends on your readers, as our guide to what counts as a good readability score explains.
Worked examples
Example 1: a very simple sentence
"The cat sat on the mat." has 6 words, 1 sentence and 6 syllables. ASL is 6 and ASW is 1.0:
206.835 − (1.015 × 6) − (84.6 × 1.0) = 116.1
The score is above 100 because every word has one syllable and the sentence is short.
Example 2: everyday instructions
"We updated the app. It now saves your work every minute, so you will not lose changes if your browser closes."
This has 21 words, 2 sentences and 28 syllables, so ASL is 10.5 and ASW is about 1.33:
206.835 − (1.015 × 10.5) − (84.6 × 1.33) ≈ 83.4 (easy)
Example 3: the same message, written two ways
Before: "The committee, having considered the recommendations submitted by the working group, which met on several occasions during the previous quarter, has decided to postpone implementation until additional consultation with stakeholders can be completed."
One 33-word sentence with many long words. Our checker scores it at about −11, well below zero.
After: "The working group met several times last quarter and sent its advice. The committee has read it. It will delay the change until it has consulted more people."
Three sentences, 28 words and mostly short words. It scores about 76.5 (fairly easy), and it says the same thing.
Syllable counts in these examples are automated estimates. A different tool might count one or two words differently and give a slightly different score.
How sentence length and syllables affect the score
Because the formula is a straight line, you can read the effect of each input directly from the numbers:
- Sentence length: every extra word in the average sentence lowers the score by about 1 point (1.015).
- Word length: every extra 0.1 syllables in the average word lowers the score by about 8.5 points (84.6 × 0.1).
So word choice has a large effect. Moving from an average of 1.4 to 1.6 syllables per word costs about 17 points, roughly the same as making every sentence 17 words longer. In practice that is why swapping a few long words for familiar short ones can raise a score as much as splitting sentences.
It also explains why technical writing tends to score low. Words such as "configuration" or "authentication" carry five syllables each, and there is often no shorter word that means the same thing.
Limitations
- It does not measure meaning. Two sentences of the same length and syllable count get the same score, even if one is clear and the other is confusing.
- Syllable counts are estimates. Software uses rules to guess syllables, and those rules disagree on some words. Different tools can give different scores for the same text.
- Formatting changes the count. Headings, bullet points and line breaks can be counted as separate sentences, which changes the average sentence length.
- Short samples are unstable. In a short sample, a single sentence or long word can move the score by many points. Score at least a few paragraphs.
- It is designed for English. The constants were set for English text, so scores for other languages are not comparable.
- It can be gamed. Chopping sentences in half raises the score without necessarily making the text clearer.
Flesch Reading Ease vs Flesch-Kincaid Grade Level
The Flesch-Kincaid Grade Level uses the same two inputs with different weights and a different scale:
Grade level = (0.39 × ASL) + (11.8 × ASW) − 15.59
It was published in 1975 by J. Peter Kincaid and colleagues, who recalculated readability formulas using tests of US Navy enlisted personnel reading Navy training material. The main differences:
- Direction: a higher Reading Ease means easier text. A higher grade level means harder text.
- Scale: Reading Ease is a score usually between 0 and 100. Grade level is a US school grade, so 8.0 means roughly that an eighth grader can understand the text.
- Weights: the two formulas balance sentence length and word length differently, so they usually move in opposite directions but not in perfect step.
Most people find the grade level easier to explain to colleagues, while the Reading Ease score shows small improvements more clearly. Looking at both, along with the other grade-level formulas, gives a better picture than either alone.
Check your own text
Paste a draft into the readability score checker to see its Flesch Reading Ease, Flesch-Kincaid Grade Level and four other readability scores, plus highlighted long sentences and suggestions based on the numbers. It runs in your browser, so your text is not uploaded. To see how your sentence lengths vary, try the sentence counter.
Sources
- Flesch, R. (1948). A new readability yardstick. Journal of Applied Psychology, 32(3), 221–233.
- Kincaid, J. P., Fishburne, R. P., Rogers, R. L., and Chissom, B. S. (1975). Derivation of new readability formulas for Navy enlisted personnel. Research Branch Report 8-75.
- Microsoft Support: Get your document's readability and level statistics.