Automated Readability Index Calculator
The Automated Readability Index (ARI) returns a US school grade level for any piece of text. Unlike Flesch-Kincaid or SMOG, it counts characters instead of syllables. This calculator rounds the result up to a whole grade.
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What the Automated Readability Index measures
ARI was developed by E. A. Smith and R. J. Senter in 1967 for the US Air Force (report AMRL-TR-66-220).
The formula combines average word length (characters per word) and average sentence length (words per sentence) and gives a single grade level. This calculator rounds the result up: a raw score of 7.2 is reported as grade 8.
How to interpret your ARI score
| ARI | Label on this calculator |
|---|---|
| Up to 5 | Elementary |
| 6–8 | Middle school |
| 9–12 | High school |
| 13–16 | College |
| 17+ | Graduate |
Because the score is rounded up, an ARI of 8 covers raw scores from just above 7 up to 8.
When to use the Automated Readability Index
- Automated scoring — it needs only character, word and sentence counts.
- Text with unusual words or names, where estimated syllable counts are least certain.
- Cross-checking — a third reading when Flesch-Kincaid and Coleman-Liau disagree.
How ARI is calculated
then rounded up to the nearest integer
Average word length (characters per word) is multiplied by 4.71. Average sentence length (words per sentence) is multiplied by 0.5. Subtract a constant to recentre the scale on US grade levels, round up to the next integer, and you have your ARI.
Both terms matter. One more character per word adds 4.71 to the raw score. Ten more words per sentence adds 5.
ARI vs other readability formulas
Coleman-Liau is ARI's closest sibling: both count characters and give US grade levels. The practical difference is that ARI gives more weight to sentence length. Writing with long sentences and short words scores higher on ARI than on Coleman-Liau; writing with short sentences and long words does the opposite.
Flesch-Kincaid Grade Level counts syllables where ARI counts characters, so the two can differ on the same passage.
SMOG and Gunning Fog count words of three or more syllables instead of characters.
Frequently asked questions
What is the Automated Readability Index?
A US grade-level readability formula that uses characters per word and words per sentence instead of syllables. E. A. Smith and R. J. Senter published it in 1967 in a report for the US Air Force.
What is a good ARI score?
It depends on your readers. No standard sets an ARI target. Lower scores suit a wider audience. This calculator rounds ARI up to a whole grade.
How is ARI different from Coleman-Liau?
Both count characters and give US grade levels. ARI gives more weight to sentence length, so it scores higher on long sentences. Coleman-Liau scores higher on long words.
Why does ARI round up?
ARI is conventionally reported as a whole number, rounded up. This calculator follows that convention, so a raw score of 7.2 shows as 8. Some tools show the decimal value instead.
Where did ARI come from?
E. A. Smith and R. J. Senter developed ARI in 1967 in a report for the US Air Force, number AMRL-TR-66-220.
How do I lower my ARI score?
Use shorter words and shorter sentences. One character less per word lowers the raw score by 4.71. Ten fewer words per sentence lowers it by 5.