Automated Readability Index (ARI) calculator
Calculate the Automated Readability Index of your text. Paste text below; your Automated Readability Index score is highlighted alongside the other formulas.
Your scores will appear here. Paste some text above, or use the sample. Everything is calculated in your browser.
The Automated Readability Index formula
ARI = 4.71 × (characters ÷ words) + 0.5 × (words ÷ sentences) − 21.43
It combines:
- Average characters (letters and numbers) per word
- Average words per sentence
Where it came from
Developed in 1967 by E. A. Smith and R. J. Senter for the US Air Force. It was designed to be calculated in real time by electric typewriters fitted with counters, so it avoids syllables entirely.
When to use it
Technical manuals and any setting where you need a fast, repeatable, fully mechanical measure.
Watch out for
ARI results can dip below zero for very simple text and can jump around on short samples. Use at least a few hundred words for a stable score.
Reading the grade
| Score | Reader |
|---|---|
| 1–5 | Primary school, age 6–11 |
| 6–8 | Middle school, age 11–14: general public |
| 9–12 | High school, age 14–18 |
| 13–16 | College |
| 17+ | Graduate / professional |
Other formulas
Flesch Reading Ease & Flesch-Kincaid · Gunning Fog Index · SMOG Index · Coleman–Liau Index
Questions people ask
What does an ARI score of 10 mean?
A reader around 10th grade (age 15–16) should be able to understand the text. ARI, like most grade formulas, maps directly to US school grades.
Why was ARI created?
The US Air Force wanted a readability measure that could be computed automatically as material was typed, so it relies on characters and words, which machines could count, instead of syllables.
Can ARI be negative?
Yes. Very short words in very short sentences can push the score below zero. Treat anything under 1 as kindergarten level.