The Flesch Reading Ease Formula and the Flesch-Kincaid Formula both use the Average Number of Words Per Sentence (Average Sentence Length) and Average Number of Syllables Per Word (Average Syllables per Word) as measures of readability.
Flesch Reading Ease
The Flesch Reading Ease Formula is:
ASL is the average sentence length (in words), and ASW is the average
syllables per word. Alternatively, it can be written more clearly as:
The Flesch Reading Ease score is interpreted as follows:
Flesch Reading Ease Score
Percentage Adults (Optimistic)
0 - 29
30 - 49
50 - 59
Senior High School, A-level
60 - 69
13 to 15 year-olds
70 - 79
80 - 89
90 - 100
We can take the Flesch Reading Ease score to indicate roughly
the percentage of the population able to read writing at this level.
However, the above table is likely to be more appropriate to the
population of the USA in the 1950's. See British American Comparison for equivalents to USA Grades.
Flesch-Kincaid Grade Level
The Flesch-Kincaid Grade Level Formula is:
ASL is the average sentence length in words, and ASW is the average
syllable length of words (as above). A clearer version is:
The Flesch-Kincaid Grade Level uses USA Grades a comparison with the British system is here.
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