There is no correct length for a sentence. A three-word sentence can land a point. A thirty-word sentence can be perfectly clear if it is built well. What matters is whether readers can follow each sentence on the first pass, and whether the lengths vary enough to keep the writing from sounding mechanical. This guide covers average sentence length, when short and long sentences work, how the answer changes for web and academic writing, and why AI drafts often end up with sentences that all sound the same.
This guide is WriterFlowLab's editorial advice. Where we cite a specific guideline, we link to its source. You can measure your own sentences with our free sentence counter.
Average sentence length
Average sentence length is the number of words divided by the number of sentences. It is the single biggest input into most readability formulas, which is why tools such as the readability score checker report it alongside the scores.
An average hides a lot, though. A passage averaging 18 words could be made of sentences that are all about 18 words long, or a mix of 6-word and 30-word sentences. The second will usually read better. So look at the spread as well as the average.
Some organisations set an upper limit rather than an average. GOV.UK, for example, has explained why 25 words is its limit: if a sentence is longer than 25 words, its writers try to break it up or condense it.
Short vs long sentences
Short sentences are easy to read and good for emphasis, warnings, instructions and key points. Too many in a row can feel choppy, and they can hide how ideas relate, because the words that link ideas (because, although, so, unless) disappear.
Long sentences can carry a chain of reasoning, a qualification or a detail that belongs with the main point. They become hard to follow when the subject and verb are far apart, when several clauses are stacked, or when the main point arrives at the end.
Compare:
Hard to follow (34 words): "Users who have not yet verified their email address, which they can do from the settings page at any time, will not be able to publish posts or invite collaborators until verification is complete."
Easier (two sentences): "Verify your email address before you publish posts or invite collaborators. You can do this at any time from the settings page."
The second version puts the action first and gives each idea its own sentence. Plain-language guidance on digital.gov makes the same point: express only one idea in each sentence.
Sentence length for web writing
People reading on screens tend to scan, and on a phone a long sentence can fill several lines before it reaches its point. For web pages, help content and emails:
- Put the main point early in the sentence.
- Split sentences that carry two separate ideas.
- Keep instructions to one action per sentence where possible.
- Use lists for three or more parallel items instead of one long sentence with commas.
- Check any sentence over 25 words, and especially any over 30. It may be fine, but it is worth a second look.
Academic and professional writing
Academic, legal and technical writing often uses longer sentences, because arguments need qualifications and terms are long. That is normal, and forcing every sentence under 15 words would distort the meaning.
Clarity still matters. A few habits help long sentences work:
- Keep the subject and the verb close together, near the start.
- Move conditions and exceptions after the main point.
- Avoid stacking several "which" and "that" clauses in one sentence.
- Follow a long, dense sentence with a shorter one that states the takeaway.
Rhythm and variety
Varying sentence length is what makes writing sound natural. A short sentence after a long one gives the reader a pause and adds emphasis. A longer sentence after several short ones can add nuance and connect ideas.
Read this passage, where every sentence is a similar length:
"Our team reviewed the new process last week. We found that it saves time on most tasks. Some steps still need clearer instructions for users. We will update the guide before the next release."
Each sentence is 8 or 9 words. It is clear, but it plods. With some variety:
"Our team reviewed the new process last week, and it saves time on most tasks. Some steps still confuse people. We will rewrite those instructions before the next release."
The meaning has not changed, but the rhythm is easier to listen to.
Why shorter is not always better
Readability formulas reward short sentences, so it is tempting to cut everything down. That can backfire:
- Lost logic. Splitting "We delayed the launch because testing found a security issue" into two sentences can drop the "because" that explains the decision.
- Choppy rhythm. A long run of very short sentences can feel abrupt or childish.
- Repetition. More sentences often means more repeated subjects ("The tool... The tool... The tool...").
Aim for sentences that are as long as the idea needs and no longer, with a mix of lengths across each paragraph.
AI-generated writing and uniform sentences
AI writing tools can produce fluent sentences, but drafts often fall into patterns that make the text feel generic:
- Similar lengths. Many sentences land in the same medium range, which gives the text a flat, even rhythm.
- Repeated structures. The same shapes recur: "Whether you are X or Y...", "It is not just X, it is Y", or three-item lists in sentence after sentence.
- Repeated openers. Several sentences start with "This", "Additionally" or "However".
A quick check is to paste the draft into the sentence counter and look at the length distribution. If almost every sentence falls into one band, vary some of them: cut a few to a short, direct statement and combine others where the ideas belong together. Our guides to fixing repetitive words and cleaning AI-generated text before publishing cover the other common patterns.
How to check your sentence lengths
- Paste your text into the sentence counter. It shows your average, your shortest and longest sentences, and how many fall into each length band.
- Open "Show each sentence" to find the longest ones quickly.
- Run the text through the readability score checker, which highlights long (21 to 30 words) and very long (31+ words) sentences in your text.
- Edit the sentences that carry more than one idea, then read the passage aloud.
The length bands in our tools (short up to 10 words, medium 11 to 20, long 21 to 30, very long 31 or more) are practical guides for spotting sentences worth a second look, not rules. Both tools run in your browser, so your text is not uploaded.
Next steps
For how sentence length feeds into readability scores, read what is a good readability score. For the next level up, see how many sentences a paragraph should have.