Automated readability index


The automated readability index is a readability test for English texts, designed to gauge the understandability of a text. Like the Flesch–Kincaid grade level, Gunning fog index, SMOG index, Fry readability formula, and Coleman–Liau index, it produces an approximate representation of the US grade level needed to comprehend the text.
The formula for calculating the automated readability index is given below:
where characters is the number of letters and numbers, words is the number of spaces, and sentences is the number of sentences, which were counted manually by the typist when the above formula was developed. Non-integer scores are always rounded up to the nearest whole number, so a score of 10.1 or 10.6 would be converted to 11.
As a rough guide, US grade level 1 corresponds to ages 6–8. Reading level grade 8 corresponds to the typical reading level of a 14-year-old US child. Grade 12, the highest US secondary-school grade before college, corresponds to the reading level of a 17-year-old.
Unlike the other indices, the ARI, along with the Coleman–Liau, relies on a factor of characters per word, instead of the usual syllables per word. Although opinion varies on its accuracy as compared to the syllables/word and complex words indices, characters/word is often faster to calculate, as the number of characters is more readily and accurately counted by computer programs than syllables. In fact, this index was designed for real-time monitoring of readability on electric typewriters.
ScoreAgeGrade Level
15-6Kindergarten
26-7First/Second Grade
37-9Third Grade
49-10Fourth Grade
510-11Fifth Grade
611-12Sixth Grade
712-13Seventh Grade
813-14Eighth Grade
914-15Ninth Grade
1015-16Tenth Grade
1116-17Eleventh Grade
1217-18Twelfth grade
1318-24College student
1424+Professor