Automated Readability Index (ARI) Calculator

Automated Readability Index calculator

ARI turns characters per word and words per sentence into a US grade level. Like Coleman-Liau it avoids syllables, but it puts more weight on sentence length.

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Automated Readability Index

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Readability scores for your text
Formula	Score	Reads as
Flesch Reading Ease	–
Flesch-Kincaid Grade	–	–
Gunning Fog	–	–
SMOG	–	– *
Coleman-Liau	–	–
Automated Readability	–	–
Dale-Chall	–

Formula

Score

Reads as

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Coleman-Liau

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Automated Readability

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Dale-Chall

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The Automated Readability Index formula

ARI = 4.71 × (characters ÷ words) + 0.5 × (words ÷ sentences) − 21.43

Characters (letters and numbers) per word, weighted by 4.71
Words per sentence, weighted by 0.5

What it counts

Characters are letters and digits inside words; punctuation and spaces are ignored.

What score to aim for

Grade 7–9 for general audiences. ARI tends to track Flesch-Kincaid closely on ordinary prose.

Limits to keep in mind

Senter and Smith’s original report rounded the result up to a whole grade; we show one decimal so small edits are visible.

Where it comes from

R. J. Senter and E. A. Smith developed ARI in 1967 for the US Air Force. The idea was to count strokes and spaces on an electric typewriter as the text was typed, so readability could be measured in real time.

Source: Senter, R. J., & Smith, E. A. (1967). Automated Readability Index. AMRL-TR-66-220, Aerospace Medical Research Laboratories, Wright-Patterson Air Force Base.

How we count syllables, sentences and words, and how our numbers compare on test passages, is documented in Readability formulas explained.

Automated Readability Index: common questions

What does ARI measure?

Average characters per word and average words per sentence, combined into a US grade level.

What is a good ARI score?

Around 7–9 for material aimed at the general public; ARI 12 roughly corresponds to a high-school senior.

Why was ARI designed for typewriters?

Counting keystrokes and spaces mechanically was feasible in the 1960s; counting syllables was not.