The optimal sentence length for readability is 15-20 words on average, with sentences rarely exceeding 30-40 words. Research from the American Press Institute shows that reader comprehension drops dramatically as sentence length increases: sentences of 8 words or fewer achieve 100% comprehension, while sentences over 43 words fall below 10% comprehension.

This guide covers research-backed sentence length guidelines to help you write clearer, more engaging content.

Sentence Length and Comprehension

Source: American Press Institute

Key insight: The relationship between sentence length and comprehension isn’t linear. Comprehension holds relatively steady until around 20 words, then drops sharply. This cliff effect means that editing a 40-word sentence into two 20-word sentences can more than double reader comprehension.

Why this matters for writers: Every sentence over 30 words is a gamble. You might convey complex information, but you risk losing half your readers before they reach the period. The safest approach is to break long sentences during editing and reserve longer structures for situations where complexity truly serves the content.

Why Sentence Length Matters for Readers

Cognitive Load and Working Memory

Readers process text through working memory, which has limited capacity. Longer sentences strain this capacity in several ways:

• More ideas to hold simultaneously
• Complex grammatical structures to parse
• Greater chance of losing track mid-sentence
• Need to re-read to understand meaning

The 7-item limit: Cognitive research suggests working memory holds approximately 7 items. Sentences that contain more than 7-10 distinct concepts overwhelm processing capacity.

Reading Speed and Flow

Sentence length directly affects reading rhythm:

Short sentences: Create quick, punchy pace. Easy to process. Build momentum.

Medium sentences: Provide comfortable reading flow with enough room for nuance and detail.

Long sentences: Slow readers down, require more concentration, and risk losing the reader’s attention before reaching the period.

The best writing varies sentence length to create natural rhythm while keeping average length in the optimal 15-20 word range.

Engagement and Completion Rates

Long sentences don’t just reduce comprehension; they reduce completion. When readers encounter a sentence they can’t parse on the first read, they face a choice: re-read it, skip it, or leave entirely. Research on web reading behavior suggests most choose to skip or leave.

Completion impact:

• Articles with shorter average sentences have lower bounce rates
• Readers are more likely to reach the call-to-action
• Social sharing increases when content is easier to read
• Comment sections are more active on readable content

This creates a compounding effect. Shorter sentences lead to better comprehension, which leads to higher engagement, which leads to more sharing and return visits.

The Historical Decline of Sentence Length

One of the most striking facts about readability is how dramatically sentence length has declined over centuries. The Oxford Guide to Plain English documents this trend:

What this tells us: Reader expectations have shifted dramatically. What qualified as clear prose in Dickens’ era now reads as dense. Modern readers, shaped by digital media and shorter attention spans, expect even tighter writing.

Practical implication: If you’re writing content that feels “literary” or “sophisticated” because of long sentences, you’re likely making it harder to read without adding value.

Modern Reading Habits Demand Shorter Sentences

The shift toward shorter sentences reflects fundamental changes in how people consume text:

Digital scanning behavior: Eye-tracking studies show readers scan rather than read linearly. Long sentences are often skipped entirely.

Mobile reading: Over 60% of web traffic comes from mobile devices. Small screens make long sentences appear even longer and more intimidating.

Information abundance: Readers have unlimited alternatives. If your content is hard to process, they’ll find easier content elsewhere.

Multitasking norms: Modern readers often consume content while doing other things. Complex sentences require undivided attention that readers rarely provide.

Optimal Sentence Length by Content Type

Web Content and Blog Posts

Target: 15-20 words average

Why shorter works online:

• Readers scan rather than read linearly
• Mobile screens make long sentences feel longer
• Competition for attention is fierce
• Comprehension matters more than literary style

Benchmark: Popular online publications average 14-18 words per sentence.

Academic and Technical Writing

Target: 20-25 words average

Considerations:

• Complex ideas sometimes require longer sentences
• Precision may demand qualifications
• Expert audiences tolerate longer sentences
• But clarity still matters

Caution: Even academic writing benefits from sentence variety. A paper averaging 30 words per sentence will exhaust readers.

Business Communication

Target: 15-18 words average

Reasoning:

• Recipients are busy and scanning
• Key information must be immediately clear
• Action items need prominence
• Professional doesn’t mean complex

Marketing and Advertising

Target: 12-15 words average

Why even shorter:

• Immediate impact required
• Skimming is standard behavior
• Emotional resonance needs clear delivery
• Every word must earn its place

Email Communication

Target: 14-18 words average

Email readers are particularly intolerant of long sentences. The inbox context creates urgency, and most emails are read on mobile devices. Business emails especially benefit from short, clear sentences that readers can process quickly while scanning.

Email-specific considerations:

• Preview pane shows only first few lines
• Recipients often skim for action items
• Long sentences feel even longer on small screens
• Clarity directly affects response rates

How to Vary Sentence Length Effectively

The Rhythm Principle

Good writing alternates between shorter and longer sentences. This creates rhythm and maintains engagement.

Example of poor rhythm: “The optimal sentence length is fifteen to twenty words. Most readers comprehend content at this length easily. Longer sentences often lose readers. This creates better engagement overall.”

Example of good rhythm: “The optimal sentence length is fifteen to twenty words. Why? Most readers comprehend content at this length easily, while longer sentences often lose them entirely. Short sentences punch. Longer ones can develop ideas with nuance and complexity when needed.”

The One-Idea Rule

Each sentence should convey one main idea. If you find yourself using multiple commas, semicolons, or conjunctions, consider splitting the sentence.

Before (42 words): “The marketing team decided to launch the campaign in Q4 because holiday spending increases consumer engagement, and they wanted to capitalize on seasonal trends while also testing new messaging that had performed well in focus groups but hadn’t been validated at scale.”

After (split into manageable pieces): “The marketing team decided to launch the campaign in Q4. Holiday spending increases consumer engagement, making it the ideal season for new initiatives. They also wanted to test messaging that performed well in focus groups but hadn’t been validated at scale.”

Strategic Use of Short Sentences

Short sentences create emphasis. Use them intentionally.

For impact: “We missed the deadline. Everything changed.”

For clarity after complexity: After a longer, detailed sentence, a short sentence lets readers catch up.

For transitions: Short sentences can signal topic shifts or section breaks.

The 20-10-30 Pattern

A useful guideline for sentence length variety:

• 20% of sentences: Under 10 words (for emphasis and rhythm)
• 60% of sentences: 10-20 words (the comfortable middle)
• 20% of sentences: 20-30 words (for complex ideas that need development)

This distribution keeps your average in the optimal range while creating natural variation. Very few sentences should exceed 30 words, and those that do should be intentional.

Common Sentence Length Mistakes

The Run-On Problem

Mistake: Connecting multiple complete thoughts with commas or conjunctions.

Example: “The project was running behind schedule, so the team worked overtime, but they still couldn’t meet the deadline, and the client was frustrated.”

Fix: “The project was running behind schedule. The team worked overtime but still couldn’t meet the deadline. The client was frustrated.”

The Parenthetical Overload

Mistake: Stuffing sentences with parenthetical asides, qualifications, and tangential information.

Example: “The software update (which was originally scheduled for March but delayed due to testing issues) will improve performance significantly, especially for users who frequently work with large files (anything over 100MB) and have been experiencing slowdowns.”

Fix: “The software update will improve performance significantly, especially for users working with large files. Originally scheduled for March, the update was delayed due to testing issues. Files over 100MB caused frequent slowdowns that this update addresses.”

The Passive Voice Trap

Mistake: Passive voice naturally adds words without adding meaning.

Example: “The report was written by the committee, and it was subsequently reviewed by management.”

Fix: “The committee wrote the report. Management reviewed it.”

Result: Same information in fewer words, with clearer attribution.

Over-Correction to Choppy Writing

Mistake: Making every sentence 5-8 words.

Example: “Sentences should be short. Very short is best. Readers like this. It’s easy to read. But it sounds robotic.”

Fix: Vary length while keeping averages in range. Some sentences can be longer when they flow naturally and serve the content.

Tools for Checking Sentence Length

Microsoft Word Readability Statistics

1. Go to File, then Options, then Proofing
2. Check “Show readability statistics”
3. Run spell check
4. View average sentence length in the results

Hemingway Editor

Free online tool that highlights sentences by difficulty:

• Yellow: Long sentences (hard to read)
• Red: Very long sentences (very hard to read)
• Target: Keep sentences below 14 words when possible

Grammarly

Premium feature shows average sentence length and flags excessively long sentences for revision.

Manual Counting

For quick checks: Count words in a sample of 10-15 sentences, calculate the average. If above 20, revise longer sentences.

Online Letter and Word Counters

Many text analysis tools provide sentence-level statistics alongside word and character counts. These tools are especially useful for checking:

• Average sentence length across your document
• Number of sentences exceeding recommended limits
• Sentence length distribution
• Comparison against readability benchmarks

For quick analysis, paste your text into an online tool and review the sentence statistics before finalizing your content.

Sentence Length for Different Audiences

General Public

Target: 14-17 words average

Average U.S. reading level is 7th-8th grade. Shorter sentences ensure broad accessibility.

Professional Audiences

Target: 17-22 words average

Can handle slightly more complexity but still value clarity and efficiency.

Expert/Academic Audiences

Target: 20-25 words average

Higher tolerance for complexity, but comprehension still drops with excessive length.

Non-Native English Speakers

Target: 12-16 words average

Simpler structures and shorter sentences significantly improve comprehension for ESL readers.

Children and Young Adult Audiences

Target: 10-14 words average

Content for younger readers should use even shorter sentences. Educational research shows that reading comprehension develops gradually, and sentence length should match the reader’s developmental stage.

Age-appropriate guidelines:

• Elementary school: 8-12 words average
• Middle school: 12-16 words average
• High school: 14-18 words average

These ranges help young readers build confidence while gradually introducing more complex sentence structures.

Frequently Asked Questions

What’s the ideal sentence length for SEO?

Search engines don’t measure sentence length directly, but readability affects engagement metrics that influence rankings. Aim for 15-20 words to keep readers on the page.

Can sentences ever be too short?

Yes. Consistent 3-5 word sentences feel choppy and robotic. Vary length for natural rhythm while keeping averages in the optimal range.

Do punctuation and sentence breaks affect readability scores?

Yes. Flesch Reading Ease and similar scores use sentence length as a primary factor. Shorter sentences directly improve these scores.

How do I fix long sentences without losing meaning?

Split at conjunctions (and, but, so), remove parenthetical asides, convert passive voice to active, and eliminate unnecessary qualifiers.

Should I count sentence length while writing?

No. Write naturally, then check sentence length during editing. Worrying about word count during drafting interrupts creative flow.

How does sentence length relate to paragraph length?

Both contribute to readability. Optimal paragraphs are 2-4 sentences. If your sentences average 20 words, paragraphs should be 40-80 words.

Key Takeaways

• Optimal average sentence length is 15-20 words for most content
• Comprehension drops from 100% at 8 words to below 10% at 43+ words
• Mean sentence length has declined historically: Chaucer (49 words) to Rowling (12 words)
• Vary sentence length for rhythm while keeping averages in range
• Split sentences at conjunctions, remove parentheticals, use active voice
• Use tools like Hemingway Editor or Word’s readability statistics to check length

Conclusion

Sentence length is one of the most controllable factors in readability. The research is clear: readers comprehend short sentences far better than long ones. Keep your average in the 15-20 word range, vary length for rhythm, and ruthlessly split sentences that exceed 30 words. Your readers will stay engaged, comprehend more, and actually finish reading. Try our free letter counter → to analyze your text structure and identify opportunities to improve readability.