Flesch Reading Ease Readability Formula

The Flesch Reading Ease readability formula calculates an index score of a text sample based on sentence length and the number of syllables.

Flesch Reading Ease is best meant for school text and is a standard used by many U.S. government agencies, including the U.S. Department of Defense. Scores range from 0-100 (the higher the score, the easier to read) and average documents should be within the range of 60-70.

The Flesch Reading Ease Formula

FI = 206.835 - (84.6*(SY/W)) - (1.015*(W/S))

Where:

FI	Flesch index score
W	Number of words
SY	Number of syllables
S	Number of sentences

Flesch Reading Ease Index Table

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

Citations

Flesch, R. How to Write Plain English.