Sentence length is the single biggest lever you have over how easy your writing is to read. Word choice matters, paragraph structure matters, but nothing wears a reader down faster than a string of long, winding sentences. The good news is that the target is simple: aim for an average of 15 to 20 words per sentence, and keep most individual sentences under 25. This guide explains where those numbers come from, why they work, and how to bring an overlong draft back into range.
The short answer: 15–20 words on average
Most readability research lands in the same place. An average sentence length of 15 to 20 words is comfortable for a general audience. Drop below 10 and prose starts to feel choppy and childish; climb above 25 and comprehension falls off a cliff.
The word average is doing important work here. You are not trying to make every sentence exactly 18 words long — that would be its own kind of monotony. You want a mix: short sentences for emphasis, medium sentences for the bulk of your argument, and the occasional longer sentence when an idea genuinely needs room. The average is what keeps the whole thing readable.
| Average sentence length | Reading experience | Best for |
|---|---|---|
| Under 10 words | Choppy, abrupt | Headlines, ad copy, emphasis |
| 11–14 words | Clear and brisk | News, web copy, instructions |
| 15–20 words | Balanced sweet spot | Most writing |
| 21–25 words | Demanding but workable | Technical and academic prose |
| 26+ words | Hard to follow | Almost nothing online |
Why long sentences hurt comprehension
Reading is an act of holding information in working memory until the sentence resolves. Every clause, qualifier, and subordinate phrase you add is one more thing the reader has to keep in their head before they reach the verb that makes it all make sense. Working memory is small — most people can hold only a handful of items at once. A 40-word sentence routinely exceeds that budget, and the reader has to back up and start again.
This is exactly what readability formulas measure. The Flesch Reading Ease score penalizes long sentences directly: the more words per sentence, the lower (harder) the score. The Flesch-Kincaid grade level does the same thing, translating sentence length and syllable count into a school grade. If your sentences are long, no amount of simple vocabulary will rescue the score.
A before-and-after example
Here is a sentence that tries to do too much:
Although the product launched in March, which was later than we had originally planned because of supply-chain delays that affected nearly every component, the team managed to hit its first-quarter revenue target, a result that surprised even the executives who had been bracing for a shortfall.
That is one 52-word sentence carrying at least four separate ideas. Split it:
The product launched in March — later than planned, thanks to supply-chain delays that hit nearly every component. Even so, the team hit its first-quarter revenue target. The result surprised even the executives, who had been bracing for a shortfall.
Same information, now three sentences averaging about 13 words each. Nothing was lost. Everything got easier to read.
How to shorten long sentences
You rarely need to rewrite from scratch. A few mechanical moves fix most overlong sentences:
1. Split at the conjunction
Sentences joined by and, but, so, or which are often two sentences wearing a trench coat. Find the joint and cut it:
- Before: “The report was finished on time, and the client approved it the next morning, but the budget had already been spent.”
- After: “The report was finished on time, and the client approved it the next morning. But the budget had already been spent.”
2. Cut the qualifiers
Words like very, really, in order to, due to the fact that, and it is important to note that add length without adding meaning. Deleting them shortens the sentence and sharpens it.
3. Turn a subordinate clause into its own sentence
If a sentence has a “which” or “that” clause trailing a complete thought, promote it:
- Before: “We hired three engineers, which allowed us to ship the feature a month early.”
- After: “We hired three engineers. That let us ship the feature a month early.”
4. Use a list
When a sentence enumerates several things, a bulleted or numbered list almost always reads better than a comma-spliced run.
When you over-correct and end up with a wall of five-word sentences, the prose turns choppy — see run-on sentences for the opposite failure mode and how to spot the seam where one sentence should become two.
It depends on the audience and medium
The 15–20 word target is a default, not a law. Adjust it for context:
- Web and mobile content: lean shorter, 12–18 words. People skim on phones, and short sentences create the white space that keeps them scrolling. This pairs naturally with shorter paragraphs — see how long a paragraph should be.
- Technical and legal writing: longer sentences (up to 25) are sometimes unavoidable when precision requires qualification. Compensate by keeping vocabulary plain.
- Children’s and plain-language content: aim for 8–12 words to match a lower reading level.
- Fiction and narrative: vary deliberately. A long, flowing sentence followed by a three-word punch is a rhythm tool, not a readability problem.
How to measure your sentence length
You can’t improve what you don’t measure, and counting by hand is tedious. Paste your draft into the sentence counter to see how many sentences you have and how they break down — it’s the fastest way to spot a paragraph that’s secretly one giant sentence. To judge the average, divide your total word count (from the word counter) by the number of sentences.
For a single number that captures the whole picture, run the text through the readability score checker. It folds average sentence length into a grade level and a reading-ease score, so you can see at a glance whether your sentences are pulling the score down. If they are, the fixes above are where to start — and the broader playbook lives in how to improve your readability score.
The bottom line
Aim for an average of 15–20 words per sentence, keep most sentences under 25, and vary the length so the rhythm doesn’t flatten. Long sentences overload working memory and drag down every readability formula, so when a sentence creeps past 25 words, look for a conjunction to split at or a qualifier to cut. Measure as you go with the sentence counter and confirm the result with the readability score checker — small changes to sentence length produce the biggest jumps in how readable your writing feels.
Frequently Asked Questions
What is the ideal sentence length for readability?
An average of 15 to 20 words per sentence, with most individual sentences staying under 25. Vary the length around that average — mix short, medium, and the occasional longer sentence — rather than making every sentence the same size.
How many words should a sentence have?
There’s no fixed number, but a good working range is 10 to 20 words for most sentences. Sentences under 10 words are great for emphasis; sentences over 25 words start to strain comprehension and should usually be split.
Why do long sentences reduce readability?
Long sentences force the reader to hold more clauses and qualifiers in working memory before the sentence resolves. When a sentence exceeds that mental budget — often around 25–30 words — readers have to reread it. Readability formulas like Flesch Reading Ease penalize long sentences directly.
What is a good average sentence length for web content?
For websites and mobile reading, aim a little shorter than usual — about 12 to 18 words on average. Short sentences create white space and keep skimming readers moving down the page.
How do I measure my average sentence length?
Count your sentences with the sentence counter and your words with the word counter, then divide words by sentences. Or paste the text into the readability score checker, which factors average sentence length into its grade-level result automatically.
Can sentences be too short?
Yes. A run of very short sentences (under 8 words each) reads as choppy and can feel abrupt or simplistic. The goal is a natural mix — use short sentences for emphasis, not for the entire piece.