Readability Checker

What is readability?

Readability is how easy a piece of text is to read and understand. Readability formulas estimate it from the length of your sentences and the length of your words, measured in syllables or letters. Long sentences and long words both push a score towards difficult.

How the checker counts

• Contractions such as don't and it's, accented words such as café and naïve, and hyphenated words such as co-operate count as one word each.
• A figure such as 30 or £1,250.00, and a short form such as e.g. or U.K., counts as one word of one syllable. Rudolf Flesch, who wrote the Reading Ease formula, counted them this way.
• A sentence ends at a full stop, question mark or exclamation mark followed by a space. The point in £3.50 does not end a sentence, and nor does the full stop in a short form such as Mr., e.g., etc., a.m. or U.S. when the sentence carries on.
• A new line also ends a sentence, so a heading or a list item counts as a sentence of its own. When the next line starts with a small letter, as in text copied from a PDF, the tool treats it as the same sentence. A line that starts with a capital letter or a figure starts a new sentence, so join the broken lines of a PDF first.
• Syllables are estimated from spelling, as most automatic checkers do. The tool counts most everyday words right, but an unusual word or a name can be out by one.
• The formulas were made for English, so scores for text in other languages mean little.

For the fairest score, paste only the running text. Flesch advised leaving out titles, headings, captions and signature lines. He built his formula on samples of 100 words, so a score for a line or two is rough.

The two Flesch formulas

Flesch Reading Ease = 206.835 - (1.015 × words per sentence) - (84.6 × syllables per word). Higher is easier. Flesch's scale runs from 0, practically unreadable, to 100, extremely easy. The tool shows a score above 100 as 100 and one below 0 as 0.

Flesch-Kincaid grade = (0.39 × words per sentence) + (11.8 × syllables per word) - 15.59. The answer is a US school grade: 8.0 means a pupil in the eighth grade can understand the text.

What the scores mean

Flesch's own scale, with the US school grade he gave each band and the reading age that grade suits:

• 90 to 100: Very easy. 5th grade, reading age 10 to 11.
• 80 to 90: Easy. 6th grade, reading age 11 to 12.
• 70 to 80: Fairly easy. 7th grade, reading age 12 to 13.
• 60 to 70: Standard, or plain English. 8th and 9th grade, reading age 13 to 15.
• 50 to 60: Fairly difficult. 10th to 12th grade, reading age 15 to 18.
• 30 to 50: Difficult. University level.
• 0 to 30: Very difficult. Best understood by university graduates.

Reading age and school grade

Grade scores follow the US school system. Most US children start kindergarten at 5 and finish grade 12 at 17 or 18, so add 5 to a grade to find the youngest reading age it suits. Grade 8 suits readers aged 13 to 14, the age of pupils in Year 9 in England. The tool shows this reading age under every grade score.

Readability formulas used

• Flesch-Kincaid Grade Level: Estimates the US school grade needed to understand the text.
• Flesch Reading Ease: Scores from 0 to 100, where higher scores mean easier reading.
• Gunning Fog Index: Estimates the years of formal education needed.
• SMOG Index: Predicts the grade needed for full understanding.
• Coleman-Liau Index: Uses letter counts instead of syllables.
• Automated Readability Index: Based on characters per word and words per sentence.

Worked example

Take this line from a formal letter: “We regret to inform you that your application has been unsuccessful on this occasion.”

1. Count: 14 words in 1 sentence, with 24 syllables. Application and unsuccessful have 4 syllables each, and occasion has 3.
2. Words per sentence: 14 ÷ 1 = 14. Syllables per word: 24 ÷ 14 = 1.71.
3. Flesch Reading Ease: 206.835 - (1.015 × 14) - (84.6 × 24 ÷ 14) = 206.835 - 14.21 - 145.03 = 47.6. The tool shows 48, which is difficult.
4. Flesch-Kincaid grade: (0.39 × 14) + (11.8 × 24 ÷ 14) - 15.59 = 5.46 + 20.23 - 15.59 = 10.1, a US 10th grader, so a reading age of 15 to 16.

Now a plainer version: “We're sorry, but your application was not successful this time.” It has 10 words and 16 syllables, so its Reading Ease is 61.3 (standard, or plain English) and its grade is 7.2, a reading age of 12 to 13. The tool's Grade Level box shows 11.7 for the first version, because it averages all five grade scores.

Use cases

• Content marketing: Check that blog posts suit your readers
• AI content review: Check AI-written text before you publish it
• Technical writing: Simplify guides for a wider audience
• Education: Match reading material to a class's reading age
• Health and legal: Make letters to patients and customers easier to follow

Tips for improving readability

• Keep sentences under 20 words on average
• Use common words instead of complex vocabulary
• Break up long paragraphs
• Use bullet points for lists
• Write in active voice
• Avoid jargon unless necessary for your audience

Questions and answers

Related tools

Need a word or character count as well? Try the Word Counter. To join the broken lines in text copied from a PDF, use the Remove All Newlines option in the Text Cleaner. Compare two drafts with Text Diff, fix capital letters with the Case Converter, or browse all text tools.

Sources, checked on 26 September 2026: Rudolf Flesch's How to Write Plain English for the counting rules, the formula and the school grades; William DuBay's The Principles of Readability for the score labels and the Fog and ARI formulas; McLaughlin (1969) for SMOG and Coleman and Liau (1975) for the Coleman-Liau index; Microsoft for the 60 to 70 and grade 7 to 8 targets; the Home Office for the reading age of 9; and GOV.UK for school years in England.