Automated readability index

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The automated readability index (ARI) 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.[1]

Score Age Grade Level
1 5-6 Kindergarten
2 6-7 First/Second Grade
3 7-9 Third Grade
4 9-10 Fourth Grade
5 10-11 Fifth Grade
6 11-12 Sixth Grade
7 12-13 Seventh Grade
8 13-14 Eighth Grade
9 14-15 Ninth Grade
10 15-16 Tenth Grade
11 16-17 Eleventh Grade
12 17-18 Twelfth grade
13 18-24 College student
14 24+ Professor


  1. ^ Senter, R.J.; Smith, E.A. (November 1967). "Automated Readability Index". Amrl-Tr. Aerospace Medical Research Laboratories (U.s.). Wright-Patterson Air Force Base: 1–14. PMID 5302480. AMRL-TR-6620. Retrieved March 18, 2012.