The ideal sentence length
There is no single correct length, but readability research and style guides point in the same direction:
- Average 15–20 words per sentence for general writing, web content and business email.
- Under 25 words for any single sentence you want readers to understand on the first pass.
- Over 35 words is a strong signal that the sentence should be split.
Government plain-language guidance points the same way: the GOV.UK style guide asks writers to keep sentences to 25 words or fewer, and the US federal plain language guidelines suggest an average of about 20 words.
Why long sentences are hard to read
Readers hold a sentence in working memory until they reach its end and can work out its meaning. Each extra clause adds something to keep track of. An often-quoted study by the American Press Institute found that readers understood almost all of a sentence of eight words or fewer, but comprehension fell steadily as sentences got longer, to well under half for sentences of around 40 words.
Long sentences also hide the main point. When a sentence contains three ideas, readers can't tell which one matters most.
How readability scores use sentence length
Most readability formulas are built on just two measurements: average sentence length and average word length. The Flesch reading ease score, for example, is:
206.835 − 1.015 × (words ÷ sentences) − 84.6 × (syllables ÷ words)
Every extra word in your average sentence lowers the score by about one point. Cutting your average from 25 words to 15 raises it by about 10 points, enough to move from “fairly difficult” to “standard”. You can test your own writing with the readability checker.
Variety matters as much as length
A page made only of 15-word sentences sounds flat and robotic. Good writing mixes lengths. Short sentences add emphasis. Longer ones carry explanation, nuance and rhythm, as long as they're clearly built. Aim for a sensible average, not a uniform length.
How to shorten a long sentence
1. Split at the conjunction
Sentences joined with and, but or which can often become two.
Before (34 words): We reviewed the survey results from all three regions and found that customers in the north were the most satisfied, which surprised the team because that region had the slowest delivery times.
After (14 + 15 words): We reviewed the survey results from all three regions. Customers in the north were the most satisfied. That surprised the team, because the north had the slowest delivery times.
2. Cut filler phrases
- “in order to” → “to”
- “due to the fact that” → “because”
- “at this point in time” → “now”
- “has the ability to” → “can”
3. Use the active voice
“The report was approved by the board” (7 words) becomes “The board approved the report” (5 words), and it's clearer about who did what.
4. Turn lists into lists
If a sentence contains four or more items, a bulleted list is easier to scan.
When longer sentences are fine
Academic, legal and literary writing often uses longer sentences, and readers of those texts expect them. Even there, a sentence should have one main idea and a clear structure. If you have to read it twice to understand it, so will everyone else.
Check your sentences
The sentence counter lists every sentence in your text with its word count, highlights sentences over 25 words in amber and over 35 words in red, and shows your average sentence length.