Automated Readability Index Calculator

The formula is 4.71 * (characters / words) + 0.5 * (words / sentences) - 21.43. Longer words and longer sentences both push the score up. The raw value is then mapped to a US grade level.

Letters and digits only, matching the pattern A to Z, a to z and 0 to 9. Spaces and punctuation are not counted, so the score reflects how long the actual words are.

A word is an unbroken run of letters or digits, so hyphenated or punctuated tokens can split. A sentence is each run of . ! or ? characters, with a minimum of one sentence for any non-empty text.

ARI uses character counts rather than syllables. Characters are counted precisely with no phonetic guessing, so the same text always yields the same index. Syllable-based formulas rely on heuristics that can disagree.

The raw index is rounded up to the next whole number, then mapped to a band. For example an index of 1.39 rounds up to 2 and shows as Grade 1-2, while 11.33 rounds up to 12 and shows as Grade 12.

Both return a US grade level, but ARI uses characters per word while Flesch-Kincaid uses syllables per word. The two grades are usually close on ordinary prose yet rarely identical, so it helps to read them together.

Yes. This page renders the unified readability checker, which lists ARI next to Flesch Reading Ease, Flesch-Kincaid, Gunning Fog, Coleman-Liau and SMOG. Those cards round each index to one decimal place for a quick side-by-side view.

Not very. On a single short sentence the words-per-sentence term swings hard, so one clause can read as a high grade. ARI is designed for paragraphs, and the score steadies as you add more sentences.

Yes. The score is computed in your browser and nothing is uploaded or stored, so you can safely paste unpublished or sensitive drafts.