Automated Readability Index Calculator
The ARI is one of the oldest and most reliable readability formulas. It uses characters per word and words per sentence to estimate U.S. grade level. Get your score instantly below.
Breakdown
What Is the Automated Readability Index?
How it works
The Automated Readability Index was introduced in 1967 and designed to be calculated by machines — hence "automated." It uses two simple measurements: average characters per word and average words per sentence, to output a U.S. school grade level.
Grade level reference
An ARI score of 1 corresponds to 1st grade (ages 6–7). A score of 8 corresponds to 8th grade (ages 13–14). A score of 12 is a high school senior (age 18). Scores above 14 correspond to college and graduate-level reading.
Original purpose
The ARI was originally developed for the U.S. Air Force to assess the readability of technical manuals and equipment documentation. It remains widely used in technical writing, military documentation, and government communications.
ARI vs Other Readability Formulas
vs Flesch-Kincaid
Both ARI and Flesch-Kincaid Grade Level return a U.S. grade level score. Flesch-Kincaid uses syllable counts; ARI uses character counts. For most texts they produce similar results, but ARI tends to be more consistent for technical writing.
vs Coleman-Liau
Both use character counts rather than syllables. Coleman-Liau measures characters per 100 words; ARI measures characters per word. They often produce very similar scores and are both well-suited for technical and scientific writing.
Best practice
Rather than relying on a single formula, compare scores across multiple formulas. When ARI, Flesch-Kincaid, and Coleman-Liau all agree, you can be confident in the grade level estimate. Our main tool runs all six formulas at once.