Writing Easily Read Text and Readability Scales - Flesch-Kincaid

The Flesch/Flesch–Kincaid readability tests are designed to indicate comprehension difficulty when reading a passage of contemporary academic English.

There are two tests, the Flesch Reading Easiness, and the Flesch–Kincaid Grade Level. Although they use the same core measures (word length and sentence length), they have different weighting factors, so the results of the two tests correlate approximately inversely: a text with a comparatively high score on the Reading Ease test should have a lower score on the Grade Level test. Both systems were devised by Rudolf Flesch.

Flesch Reading Ease
In the Flesch Reading Ease test, higher scores indicate material that is easier to read; lower numbers mark passages that are more difficult to read. The formula for the Flesch Reading Ease Score (FRES) test is;

Scores can be interpreted as shown in the table below.

Score Notes

• 90.0–100.0 easily understandable by an average 11-year-old student
• 60.0–70.0 easily understandable by 13- to 15-year-old students
• 0.0–30.0 best understood by university graduates

Reader's Digest
Reader's Digest magazine has a readability index of about 65, Time magazine scores about 52, an average year 7 student's (eleven years old) written assignment has a readability test of 60-70 (and a reading grade level of 6-7) and the Harvard Law Review has a general readability score in the low 30s.

The highest (easiest) readability score possible is around 120 (e.g. every sentence consisting of only two one-syllable words); there is no theoretical lower bound on the score—this sentence, for example, taken as a reading passage unto itself, has a readability score of about 48.23. This paragraph has a readability score of about 50.91.

Government Agencies

Many government agencies require documents or forms to meet specific readability levels.
The U.S. Department of Defense uses the Reading Ease test as the standard test of readability for its documents and forms. Florida requires that life insurance policies have a Flesch Reading Ease score of 45 or greater.

Use of this scale is so ubiquitous that it is bundled with popular word processing programs and services such as Google Docs, KWord, Pages, Lotus Symphony, Microsoft Office Word, WordPerfect, and WordPro.

Long words affect this score significantly more than they do the grade level score.

Flesch–Kincaid Grade Level
These readability tests are used extensively in the field of education. The "Flesch–Kincaid Grade Level Formula" translates the 0–100 score to a U.S. grade level, making it easier for teachers, parents, librarians, and others to judge the readability level of various books and texts.

It can also mean the number of years of education generally required to understand this text, relevant when the formula results in a number greater than 12. The grade level is calculated with the following formula:

The result is a number that corresponds with a grade level. For example, a score of 8.2 would indicate that the text is expected to be understandable by an average student in 8th grade (usually around ages 13–14 in the United States of America). This page has the score of 12.5.

The lowest grade level score in theory is -3.40, but, since there are few real passages that have every sentence consisting of two one-syllable words, this rarely occurs in practice.

Green Eggs and Ham by Dr. Seuss comes close, averaging 5.7words per sentence and 1.02 syllables per word, with a grade level of -1.3. (Most of the 50 used words are monosyllabic; "anywhere", which occurs 8 times, is an exception.)