Readability Score

How the Readability Checker works

Readability score: what the formulas actually count

Every readability formula here reduces a text to two or three counts: how long the sentences are, how long the words are, and sometimes how many words have three or more syllables. None of them reads for meaning, grammar or tone. They measure the load that long sentences and long words put on a reader. That load is the part of difficulty that most reliably predicts whether people finish a page and understand it.

The formulas side by side

For example, Flesch reading ease is 206.835 − 1.015 × (words per sentence) − 84.6 × (syllables per word). Every extra word per sentence costs about one point, and every extra tenth of a syllable per word costs eight and a half. Word length has far more effect on the score than sentence length.

A worked example

This sentence is the kind found in strategy documents: "Notwithstanding the aforementioned considerations, the organisation's comprehensive implementation strategy necessitates substantial interdepartmental collaboration and continuous evaluation of operational effectiveness." It has 19 words, 71 syllables and 15 complex words. It scores −128.6 on Flesch reading ease and grade 35.9 on Flesch–Kincaid. The formulas are not meant for text this dense, so the numbers run far past their scales.

The plain version reads: "Our plan will only work if departments work closely together. We will also keep checking how well each part is doing, and change course when something is not working." It has 29 words in 2 sentences and scores 72.5, fairly easy. Its Flesch–Kincaid grade is 6.7, and the consensus is grade 9. It says the same thing, and far more readers will get to the end of it.

How to read the result

• Flesch reading ease comes with a band. 60 to 70 is plain English, roughly what a 13 to 15-year-old reads comfortably. Scores below 0 or above 100 are possible with very short or very dense samples.
• Flesch–Kincaid grade is a US school grade, shown with the matching age: grade 8 is about age 13 to 14. Above grade 12 it reads College, and above 16 Graduate.
• Consensus grade level averages Flesch–Kincaid, Gunning fog, SMOG, Coleman–Liau and ARI. It is the steadiest single figure, because each formula's quirks partly cancel out.
• The table lists every score along with the raw counts: words, sentences, syllables, words per sentence, syllables per word and the share of complex words. These show what to fix. A high words-per-sentence figure means split sentences. A high syllables-per-word figure means swap long words for short ones.

Where readability targets are used

• GOV.UK content design guidance aims for a reading age of 9, because plain text is faster for every reader, experts included.
• Patient information. The American Medical Association and the US National Institutes of Health recommend writing health materials at grade 6 to 8. SMOG is the formula most often used in health research.
• Insurance. Florida law requires most personal insurance policies to reach a Flesch reading ease score of at least 45, and several other US states have similar rules.
• Defence manuals. Flesch–Kincaid and ARI were both built to check technical manuals for US military readers, and Flesch–Kincaid is still part of US military writing standards.
• Swedish and European schools use LIX because it counts letters rather than syllables, so it works across languages.

Tips and pitfalls

• Score at least 100 words. One short sentence can swing any formula wildly, as the examples above show.
• Syllables are estimated. The counter uses spelling rules, not a dictionary, so names and unusual words can be a syllable out. Over a page the errors average out.
• Lists and headings distort the score. Bullet points without full stops run together into one long "sentence". Score body text, or add full stops to the bullets before pasting.
• Do not write to the formula. Chopping every sentence to six words raises the score but reads like a telegram. Aim for an average of 15 to 20 words, with some variety.
• Specialist words are sometimes right. A medical audience needs "myocardial infarction". Grade the text for the reader you have, not the lowest one imaginable.
• English only. The weights were fitted to English. The scores mean little for other languages, except LIX.

Check the length with the word counter and see how long the text takes with the reading time calculator. The keyword density checker shows which terms dominate a page.

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