Like other popular readability tests, the Bormuth Readability Index
calculates a reading grade level required to read a text based on two factors: 1)
character count (average length of characters) rather than syllable count; and 2)
average number of familiar words in the sample text. The Bormuth Readability Index uses the Dale-Chall word list to count familiar words in samples of text. Initially, Professor John R. Bormuth of the University of Chicago developed this formula to evaluate academic documents and school textbooks.
This formula works reliably on texts above 4th grade level.
Typically, the Bormuth Readability Index
outputs a grade level that closely matches the adjusted grade level from the new Dale-Chall Readability Formula
. The differences between the two formulas are that the Bormuth Readability Index relies on character count instead of syllable count; and instead of calculating a percent of difficult words, it calculates the average of familiar words in the text.
The Bormuth Readability Index is sometimes called The Bormuth Formula
, the Bormuth Grade Level Formula
, or Degrees of Reading Power
. (The Bormuth Readability Index was adapted into the Degrees of Reading Power used by the College Entrance Examination Board in 1981.)
Use the following formula to calculate
the Bormuth Readability Index
GL = 0.886593 - (AWL x 0.03640) + (AFW x 0.161911) - (ASL x 0.21401) - where: GL
(ASL x 0.000577) -
(ASL x 0.000005)
: Grade level needed to read the text. AWL
: average word length or number of characters per word (number of characters divided by the number of words) AFW
: average familiar words per word (the number of words in the Dale-Chall list of 3,000 simple words divided by the number of words) ASL
: average sentence length in words or average number of words in sentence (number of words divided by the number of sentences)
The Bormuth Readability Index outputs a number that
correlates to a U.S. grade level. For example, a result of 10.6 means students in 10th grade and above can read and comprehend the text. Unlike the new Dale-Chall Readability Formula which outputs an adjusted number that you must match to a number on an adjusted grade level table, the Bormuth Readability Index does not require you to use a table to determine an adjusted grade level.