Ideal Sentence Length: Aim for 15 to 20 Words
Average sentence length is the single biggest lever on readability. Aim for 15 to 20 words. Anything above 25 starts losing readers; below 10 reads choppy.
The short answer
For most web, business, and journalistic writing, aim for an average sentence length of 15 to 20 words. The Flesch-Kincaid formula penalizes sentences over that range and rewards mixed-length prose with a baseline near 17.
Why averages, not maxes? Variety matters. A page of 17-word sentences reads monotonously. A page that swings from 7-word punches to 28-word setups feels alive.
What the research actually says
The American Press Institute found that comprehension drops sharply once sentences pass 25 words:
- 8-word sentences: ~100% comprehension
- 14-word sentences: ~90% comprehension
- 28-word sentences: ~50% comprehension
- 43-word sentences: <10% comprehension
That's not a smooth curve. There's a cliff around 25 to 28 words where readers start losing the subject of the sentence by the time they reach the verb.
When long sentences earn their keep
Long sentences aren't bugs. They work when:
- You're listing parallel items that share a common predicate; splitting them feels stilted.
- You're building a rhythm that a short sentence will then punctuate. The setup needs the length.
- The reader is an expert in your topic and a longer construction packs more meaning per word than three shorter ones.
The mistake is reaching for length unconsciously. Edit any sentence over 25 words by asking: does this need to be one sentence, or am I just running out of breath?
How to fix overlong sentences
- Find the second subject. If the sentence has two, split there.
- Find the conjunction. "And", "but", and "because" are natural break points; replace one with a period.
- Remove qualifiers. "Often", "generally", "in most cases" rarely add information. Cutting them shaves 5 to 10 words off a long sentence with no loss.
- Lead with the verb. Passive constructions ("It is widely believed that…") add 4 to 6 dead words at the front. Rewrite to active voice.
Use the sentence counter
Our sentence counter shows your average words-per-sentence live and lists every sentence over 25 words. Skim the flagged list at the end of a draft; it's the fastest way to find the worst offenders.
Takeaway
Aim for an average around 17 words. Treat 25 as the cliff. Mix lengths deliberately. The shortest sentence in this article is two words. The longest is 28. That's the range.
WordCounters Editorial Team
Linguists, editors & engineersA small team of writers, editors, and engineers maintaining WordCounters.app. We test every claim against current platform documentation and update posts when the underlying rules change.