Automated Readability Index (ARI) Calculator

The Automated Readability Index, or ARI, is a score that estimates which US school grade level can comfortably read a piece of text. Writers, teachers and editors use it to check whether their writing matches their audience — a grade-6 text for general readers, a grade-12 text for older students. This free ARI calculator works it out instantly: paste your text, click one button, and read the score and reading level.

ARI is one of the oldest readability formulas, and it has a practical advantage over some others: it counts characters rather than syllables, so it is easy to compute and works on any text, including technical writing full of long words.

How to calculate the ARI of your text

Paste your text into the calculator. A paragraph or more gives a steadier score than a single sentence.
Click “Calculate ARI”.
Read the ARI score, the reading level, and the reading note shown on the page.
Edit your text — shorter sentences and shorter words lower the score — and calculate again to see the change.

The ARI formula, and a worked example

ARI is calculated as: 4.71 × (characters ÷ words) + 0.5 × (words ÷ sentences) − 21.43. The result roughly matches a US grade level. Take a short passage with 500 characters, 100 words and 5 sentences. Characters per word is 500 ÷ 100 = 5.0, and 4.71 × 5.0 = 23.55. Words per sentence is 100 ÷ 5 = 20, and 0.5 × 20 = 10. Then 23.55 + 10 − 21.43 = 12.12, so the passage scores about 12.1 — roughly grade 12, or a 17–18-year-old reader. Now split those long sentences in half, giving 10 sentences instead of 5: words per sentence falls to 10, the second term falls to 5, and the score drops to about 7.1. The same words, cut into shorter sentences, read five grade levels easier — which is why sentence length is the fastest lever when a text scores too high.

What the score means

Scores around 1–6: very easy reading, suitable for young readers and broad general audiences.
Scores around 7–9: plain everyday English, the range most public information should aim for.
Scores around 10–12: high-school level, fine for older students and specialist readers.
Scores above 13: university level and beyond; general readers will struggle, and editing is usually worth it.

When to use ARI instead of another formula

ARI pairs naturally with the other readability formulas on this site. Flesch-Kincaid also gives a grade level but counts syllables, which makes it behave differently on technical text full of long but familiar words. The Gunning Fog index penalises long sentences and words of three or more syllables, while SMOG focuses on polysyllables across a sample. Because ARI counts characters, it is the most stable choice for short or technical passages, and the most predictable when you are testing edits: shorten a sentence and the score moves in a direction you can calculate. Comparing two or three formulas on the same passage gives a fairer picture than trusting any single number.

Honest limitations

ARI measures sentence and word length, not meaning. A short, clear sentence about a hard idea can score “easy” while still being difficult to understand.
Very short texts give jumpy scores. A single sentence is not a fair sample of a document.
Lists, headings and bullet points distort the counts, because the formula assumes ordinary sentences. Score body paragraphs, not a whole page layout.
The grade levels are US school grades, so they map only loosely onto other countries’ systems.

ARI calculator – frequently asked questions

What is a good ARI score?

For general readers, aim for roughly 7–9. For children, lower. For academic readers, higher scores are acceptable, but anything above 13 will exclude most general readers.

Does ARI count syllables?

No. ARI uses characters per word and words per sentence, which is what sets it apart from syllable-based formulas like Flesch-Kincaid.

Do I need to install anything?

No. The calculator runs in your browser on a phone, tablet or computer.

Is my text stored anywhere?

No account is needed and nothing is published. The calculation happens on the page for your own use.

Related tools: Flesch-Kincaid readability calculator, Gunning Fog index calculator and readability checker for comparing formulas.

Embed this tool on your website — free

Copy the code below to add this working tool to your own page. A small credit link stays with it — that’s all we ask.

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    function countWords(text) {
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    function countSentences(text) {
        return text.split(/[.!?]+/).filter(sentence =&gt; sentence.length &gt; 0).length;
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    function countSyllables(word) {
        word = word.toLowerCase();
        if (word.length &lt;= 3) return 1;
        const syllables = word.match(/[aeiouy]{1,2}/g);
        return syllables ? syllables.length : 0;
    }

    function calculateARI() {
        const text = document.getElementById('inputText').value;

        // Calculate basic stats
        const characters = countCharacters(text);
        const words = countWords(text);
        const sentences = countSentences(text);
        const syllables = text.split(/\s+/).reduce((acc, word) =&gt; acc + countSyllables(word), 0);

        // Update stats display
        document.getElementById('charCount').textContent = characters;
        document.getElementById('wordCount').textContent = words;
        document.getElementById('sentenceCount').textContent = sentences;
        document.getElementById('syllableCount').textContent = syllables;

        // Calculate ARI score
        const ariScore = calculateARIScore(characters, words, sentences);

        // Update results display
        document.getElementById('ariScore').textContent = ariScore.toFixed(2);
        document.getElementById('readingLevel').textContent = getReadingLevel(ariScore);
        document.getElementById('readingNote').textContent = getReadingNote(ariScore);
    }

    function calculateARIScore(characters, words, sentences) {
        if (words === 0 || sentences === 0) return 0;
        const averageCharsPerWord = characters / words;
        const averageWordsPerSentence = words / sentences;
        return (4.71 * averageCharsPerWord) + (0.5 * averageWordsPerSentence) - 21.43;
    }

    function getReadingLevel(ariScore) {
        const levels = [
            &quot;Kindergarten&quot;, &quot;1st Grade&quot;, &quot;2nd Grade&quot;, &quot;3rd Grade&quot;, &quot;4th Grade&quot;,
            &quot;5th Grade&quot;, &quot;6th Grade&quot;, &quot;7th Grade&quot;, &quot;8th Grade&quot;, &quot;9th Grade&quot;,
            &quot;10th Grade&quot;, &quot;11th Grade&quot;, &quot;12th Grade&quot;, &quot;College Level&quot;
        ];
        const index = Math.floor(ariScore) - 1;
        return levels[index] || &quot;College Level&quot;;
    }

    function getReadingNote(ariScore) {
        if (ariScore &lt; 1) return &quot;Very easy to read.&quot;;
        if (ariScore &lt;= 6) return &quot;Easy to read.&quot;;
        if (ariScore &lt;= 12) return &quot;Moderately difficult to read.&quot;;
        return &quot;Difficult to read.&quot;;
    }
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<p><a href="https://ilmhunt.com/automated-readability-index-ari-calculator/" target="_blank" rel="noopener">Automated Readability Index (ARI) Calculator</a> by <a href="https://ilmhunt.com/" target="_blank" rel="noopener">IlmHunt</a> — free online tools</p>