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Flesch Reading Ease Formula is considered as one of the oldest and most accurate
readability formulas. Rudolph Flesch, an author, writing consultant, and a supporter of
the Plain English Movement, developed this formula in 1948. Raised in Austria, Rudolph
Flesch studied law and earned a Ph.D. in English from the Columbia University. Flesch,
through his writings and speeches, advocated a return to phonics. In his article, A New
Readability Yardstick, published in the Journal of Applied Psychology in 1948, Flesch
proposed the Flesch Reading Ease Readability Formula.
The Flesch Reading Ease Formula is a simple approach to assess the grade-level of
the reader. It’s also one of the few accurate measures around that we can rely on without
too much scrutiny. This formula is best used on school text. It has since become a
standard readability formula used by many US Government Agencies, including the US
Department of Defense. However, primarily, we use the formula to assess the difficulty of
a reading passage written in English.
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| The Flesch Reading Ease Readability Formula
The specific mathematical formula is:
RE = 206.835 – (1.015 x ASL) – (84.6 x ASW)
RE = Readability Ease
ASL = Average Sentence Length (i.e., the number of words divided by the number
of sentences)
ASW = Average number of syllables per word (i.e., the number of syllables divided
by the number of words)
The output, i.e., RE is a number ranging from 0 to 100. The higher the number, the
easier the text is to read.
• Scores between 90.0 and 100.0 are considered easily
understandable by an average 5th grader.
• Scores between 60.0 and 70.0 are considered
easily understood by 8th and 9th graders.
• Scores between 0.0 and 30.0 are considered
easily understood by college graduates.
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| If we were to draw a conclusion from the Flesch Reading Ease Formula, then the
best text should contain shorter sentences and words. The score between 60 and 70 is
largely considered acceptable. The following table is also helpful to assess the ease of
readability in a document:
90-100 : Very Easy
80-89 : Easy
70-79 : Fairly Easy
60-69 : Standard
50-59 : Fairly Difficult
30-49 : Difficult
0-29 : Very Confusing
Though simple it might seem, the Flesch Reading Ease Formula has certain
ambiguities. For instance, periods, explanation points, colons and semicolons serve as
sentence delimiters; each group of continuous non-blank characters with beginning and
ending punctuation removed counts as a word; each vowel in a word is considered one
syllable subject to: (a) -es, -ed and -e (except -le) endings are ignored; (b) words of three
letters or shorter count as single syllables; and (c) consecutive vowels count as one
syllable.
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