How are the Flesch-Kincaid and Flesch Reading Ease scores calculated?
The Flesch-Kincaid (FK) and Flesch Reading Ease (FRE) scores are calculated using the formulas below. These formulas factor in two variables: the average number of syllables per word (ASW) in texts of about 100 words and average sentence length (ASL) measured in terms of the number of words per sentence.
Flesch-Kincaid Grade Level = (0.39 * ASL) + (11.8 * ASW) -15.59
Flesch Reading Ease = 206.835- (84.6 * ASW) - (1.015 * ASL)
ASW: Average number of syllables per word (in a 100-word chunk of text)
ASL: Average sentence length (number of words per sentence)
Both FK and FRE formulas require the counts of the average number of syllables per word and average sentence length to be done in 100-word chunks of text. Additionally, FK and FRE formulas rely on sentence-ending punctuation to determine the number of words used in analysis and where to demarcate chunks of text. The FK and FRE analyses report the total number of words submitted but only analyze the words within sentences.
Using the words within sentences, the tool must create blocks of approximately 100 words. Of course, not all text is usually organized into neat groups of 100 words.
- When the text analyzed has more than 100 words, the tool groups the sentences as close to 100 words as possible. For multiple groups of 100, the ASW and ASL is calculated for each group of approximately 100 words and then averaged for use in the formula.
- When the text analyzed has less than 100 words, all the words are calculated. However, the formula assumes 100 words so your score may be less accurate.
Results
The Flesch-Kincaid Grade Level score translates into a numerical grade, e.g. a score of 6.8 is equivalent to 6th grade reading level in the United States.
The Flesch RE score maps to a reading ease index of 0 to 100.