What is a readability score?
A readability score estimates how hard a text is to read from two things: how long the sentences are and how long the words are. Long sentences and long words make text harder. That's all the formulas can see. They don't judge whether the writing is clear, accurate or well organised.
Used that way, as a quick signal rather than a verdict, a score is a fast check on whether a draft has drifted into long, dense sentences.
What is a good Flesch Reading Ease score?
The Flesch Reading Ease score runs from 0 to 100, where higher is easier. A score of 60 to 70 is plain English that most adults read comfortably. 70 and above is easy to read. Below 50 is fairly difficult, and below 30 is the territory of academic papers and legal text.
For most websites, blogs and marketing copy, 60 or above is a sensible target. Technical documentation for specialists can reasonably score lower, because the subject needs precise, longer terms.
- 90 to 100
- Very easy. Understood by an average 11-year-old.
- 60 to 70
- Plain English. Easily understood by 13 to 15-year-olds.
- 30 to 50
- Difficult. College level.
- 0 to 30
- Very difficult. Best understood by university graduates.
The readability formulas, explained
Each formula weighs sentence and word length differently. The grade-level formulas return a US school grade: 8 means an eighth-grader, about 13 to 14 years old, should follow it.
- Flesch-Kincaid Grade Level
- Uses words per sentence and syllables per word. Developed for the US Navy in 1975 and still the most widely quoted grade level.
- Gunning Fog Index
- Uses sentence length and the share of complex words with three or more syllables. A Fog of 12 or more is hard for a general audience.
- SMOG Index
- Counts words of three or more syllables. It was designed for samples of 30 sentences, so treat it as rough on shorter text.
- Coleman-Liau Index
- Uses characters per word instead of syllables, which makes it less sensitive to how syllables are counted.
- Automated Readability Index (ARI)
- Also uses characters per word and words per sentence. Built to be calculated by machine.
What reading level should I write at?
Write for the reader you have. For a general audience, an eighth or ninth-grade level is a common target, and it doesn't mean simple ideas. It means short sentences and familiar words, which busy experts appreciate as much as anyone.
Many public-sector writing guides ask for plain language for exactly this reason: clear text works for everyone, including people reading in a second language or on a phone between other things.
Does readability affect SEO?
Not directly. Google has said it doesn't use a readability score as a ranking factor, and no formula can tell it whether a page is helpful. Readability matters because of people: a page that's easier to read is more likely to answer the visitor's question before they give up and go back to the results.
Google's guidance on helpful content asks whether a page leaves readers feeling they've learned enough to reach their goal. Clear writing makes that more likely, which is the honest reason to care about it.
How to improve readability
Start with the sentences the checker lists, then work through the rest of the draft.
- 1Split any sentence over 25 words, usually at an "and", "but" or "which"
- 2Swap long words for short ones: use for utilise, help for facilitate, start for commence
- 3Put one idea in each sentence and the main point first
- 4Use active voice so it's clear who does what
- 5Break long paragraphs into two to four sentences
- 6Add subheadings and lists so skimmers can find their place
Why formulas can mislead
Formulas count, they don't understand. A short sentence full of jargon can score well, and a clear explanation of a technical term can score badly because the term has many syllables. Syllable counts are also estimated, so scores can vary slightly between tools.
Use the score to compare drafts of the same text, and to find outliers. Read the result aloud before you trust it.