Text & writing
What Is a Good Average Sentence Length?
Average sentence length is one of the simplest measures of how demanding a piece of writing is — and one of the most used, from plain-language style guides to classic readability formulas. This guide explains how to calculate it, what published guidance recommends, and how to read your own number.
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How average sentence length is calculated
Average sentence length is total words divided by total sentences. A 300-word passage with 15 sentences averages 20 words per sentence. The Sentence Counter shows this figure as “average words per sentence”, rounded to one decimal place, using its word and sentence counts.
Because both inputs come from counting rules, the average inherits their edge cases: headings and list items count as short sentences, which pulls the average down, and an abbreviation that splits a sentence does the same. For the most meaningful number, measure running prose only.
What published guidance recommends
Style guides for public information favor short sentences. GOV.UK’s guidance for writing on the UK government website tells writers to try to split up sentences that are over 25 words long, and pairs that with advice to keep paragraphs to no more than five sentences.
Guidance like this sets a ceiling for individual sentences rather than a target average; writing that follows it usually averages well below the ceiling, because short and medium sentences balance the occasional longer one.
How readability formulas use it
Classic readability formulas combine average sentence length with word length. The Flesch Reading Ease score is 206.835 − 1.015 × (words per sentence) − 84.6 × (syllables per word), and the Flesch–Kincaid Grade Level is 0.39 × (words per sentence) + 11.8 × (syllables per word) − 15.59.
In both, longer sentences make text score as harder to read. For example, holding syllables per word steady, raising the average from 15 to 25 words per sentence adds about 3.9 grade levels in Flesch–Kincaid. That is why cutting long sentences is often the quickest way to improve a readability score.
Reading your number
These bands are a rule of thumb, not a standard. Academic, legal, and literary writing can run longer by convention and still be excellent for its readers.
| Average | What it usually means |
|---|---|
| Under 10 | Very short sentences — common in instructions and lists, or a sign that headings and bullets are included in the count. |
| About 10–20 | Typical of clear, general-audience prose. |
| About 20–25 | Getting denser; fine for expert readers, worth reviewing for a general audience. |
| Over 25 | Many sentences exceed common plain-language ceilings — look for ones to split. |
An average hides the outliers
Two passages can share an average of 18 words while one mixes 8- and 30-word sentences and the other repeats 18-word sentences. The average will not tell you which sentence is the problem. When your average is high, look for the few longest sentences — they usually account for most of it.
Good Average Sentence Length FAQ
- How do I calculate average sentence length?
- Divide the total number of words by the total number of sentences. The Sentence Counter does this automatically and shows it as average words per sentence.
- What is the maximum recommended sentence length?
- There is no universal maximum, but plain-language guidance commonly sets a ceiling around 25 words. GOV.UK, for example, advises splitting sentences over 25 words long.
- Why is my average so low?
- Headings, list items, and captions each count as a sentence, which drags the average down. Count only running prose for a representative number.
- Does a lower average always mean better writing?
- No. Very short sentences throughout can feel choppy and disconnected. The goal is clarity for your reader, usually with a mix of lengths.
- How does sentence length affect the Flesch–Kincaid grade?
- Each extra word in the average sentence adds 0.39 to the grade level, so increasing the average by 10 words raises the grade by about 3.9 when word length stays the same.
Related guides
- Short vs. Long SentencesWhen short sentences work, when long sentences earn their length, and how to split, combine, and vary sentences to make writing easier to read, with before-and-after examples.
- How Sentence Detection WorksThe punctuation rules sentence counters use, how abbreviations, decimals, ellipses, quotes, and lists are handled, and where every rule-based counter struggles.
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