Email Subject Line Length: Optimal Characters for Higher Open Rates
The optimal email subject line length is 36-50 characters for the best open rates. Research shows personalized subject lines achieve 30.5% higher open rates (Backlinko), and 47% of recipients open emails based on subject line alone. Different email clients display varying amounts—iPhone Mail shows ~40 characters, Gmail app shows ~37, Android shows 33-43, and Desktop Gmail shows ~70. Writing subject lines that work across all devices means front-loading your message in the first 37 characters.
This guide covers email subject line best practices with data-backed recommendations for maximum open rates.
Email Subject Line Character Limits
Display Limits by Client/Device
| Email Client | Characters Displayed |
|---|---|
| iPhone Mail | ~40 chars |
| Gmail app (mobile) | ~37 chars |
| Android | 33-43 chars |
| Desktop Gmail | ~70 chars |
| Outlook (desktop) | ~60 chars |
| Apple Mail (desktop) | ~70 chars |
Safe universal limit: 37 characters ensures visibility on most mobile devices
Technical vs. Practical Limits
Technical: Most email systems allow 78+ characters in subject lines Practical: 36-50 characters for readability and cross-device display Optimal: 36-50 characters with key information first
Open Rates by Subject Line Length
Research Data
Key findings:
- Optimal length: 36-50 characters for best open rates
- Personalized subject lines: 30.5% higher open rates (Backlinko)
- 47% of recipients open emails based on subject line alone
| Subject Length | Performance |
|---|---|
| 36-50 chars | Best open rates |
| Under 36 chars | May lack context |
| Over 50 chars | Truncated on mobile |
| Over 70 chars | Truncated everywhere |
Key finding: Balance brevity with enough context. Personalization matters more than length.
Why Shorter Works
Psychological factors:
- Curiosity gap with less information
- Easier to process quickly
- Stands out among longer subjects
- Mobile-optimized by default
Practical factors:
- No truncation on any device
- Complete message visible
- Clear, focused communication
The Preheader Factor
What Is Preheader Text?
Definition: Text that appears after/below the subject line in inbox preview Also called: Preview text, snippet text
Character limits:
- iPhone: ~37-55 characters
- Gmail: ~90 characters
- Outlook: Varies
Using Preheader Strategically
Extend your subject line:
- Subject: “Your order shipped” (18 chars)
- Preheader: “Track your package and get delivery updates” (44 chars)
- Combined: Full context in preview
Best practice: Write subject and preheader as a pair.
Preheader Length Recommendations
Optimal: 40-100 characters Minimum: 30 characters (avoid “View in browser” default) Maximum: 100-130 characters (longer gets cut)
Subject Line Best Practices
Front-Load Key Information
Structure:
[Most important info] [Supporting detail]
Examples:
- ✓ “50% off ends tonight - exclusive member access”
- ✗ “Exclusive member access to our special 50% off sale ending tonight”
Word Count Guidelines
Optimal: 6-10 words Research: 6-10 word subject lines achieve optimal open rates
Word count breakdown:
| Words | Character Equivalent |
|---|---|
| 3-4 words | ~15-25 chars |
| 5-6 words | ~25-35 chars |
| 7-8 words | ~35-45 chars |
| 9-10 words | ~45-55 chars |
Effective Subject Line Formulas
Urgency + Benefit: “Last chance: 40% off ends at midnight” (37 chars)
Question: “Ready to upgrade your morning routine?” (38 chars)
List/Number: “5 ways to boost productivity today” (35 chars)
Personalization: “[Name], your exclusive offer inside” (~35 chars)
Direct benefit: “Your free guide is ready to download” (36 chars)
Mobile Optimization
Mobile-First Writing
Why mobile matters:
- 60%+ of emails opened on mobile
- Smallest display limits
- Quick scanning behavior
Mobile-first approach:
- Write for 33-40 characters
- Verify on desktop (will look complete)
- Test on actual mobile devices
Testing Across Devices
Before sending:
- Send test to yourself
- Check on phone (portrait and landscape)
- Check on tablet
- Check on desktop clients you know recipients use
A/B Testing Subject Lines
What to Test
Length variations:
- Short (under 30 chars) vs. medium (30-50)
- With vs. without preheader optimization
Format variations:
- Question vs. statement
- With vs. without emoji
- Personalization vs. generic
- Urgency vs. curiosity
Testing Methodology
Sample size: Test with statistically significant portion (usually 10-20% of list) Wait time: 2-4 hours for results Measure: Open rate as primary metric
Industry-Specific Considerations
E-commerce
What works:
- Discounts upfront: “40% off today only”
- Product mentions: “New arrivals you’ll love”
- Urgency: “Selling fast - don’t miss out”
Optimal length: 25-40 characters
B2B/Professional
What works:
- Value proposition: “Increase sales by 25%”
- Industry relevance: “New marketing trends 2026”
- Personalized: “For [Company] marketing team”
Optimal length: 35-50 characters (can go slightly longer)
Newsletters
What works:
- Content hints: “This week: AI tools, SEO tips, more”
- Issue numbers: “Weekly digest #147”
- Curiosity: “You won’t believe what worked”
Optimal length: 30-45 characters
Common Subject Line Mistakes
Too Long
Problem: “We’re excited to announce our biggest ever summer sale with discounts up to 70% off across all departments”
Fix: “Summer sale: Up to 70% off everything”
Vague/Generic
Problem: “Monthly newsletter”
Fix: “3 SEO tactics that doubled our traffic”
All Caps
Problem: “HUGE SALE TODAY ONLY”
Fix: “Huge sale - today only” (or use selective caps: “HUGE sale: Today only”)
Spam Trigger Words
Avoid or use carefully:
- FREE (especially in all caps)
- Act now
- Limited time
- Click here
- $$$ or excessive punctuation
Frequently Asked Questions
What’s the best subject line length for email?
36-50 characters is optimal for best open rates. Personalized subject lines achieve 30.5% higher open rates than non-personalized ones.
Does email client matter for subject line length?
Yes, significantly. Gmail mobile shows ~37 characters while desktop Outlook shows 60+. Write for the smallest common display (33 characters) for universal readability.
Should I use emojis in subject lines?
Emojis can increase open rates in some industries (retail, lifestyle) but may hurt in others (B2B, finance). Test with your audience.
How does preheader text affect subject line strategy?
Preheader extends your subject line. Write shorter subjects and use preheader for supporting detail, creating a complete message across both.
Do personalization tokens affect character count?
Yes. “[Name]” might become “Alexandra” (9 chars). Account for the longest likely substitution.
Are there any hard character limits for subject lines?
Most email systems support 78+ characters, but readability and display limits make 50-60 the practical maximum.
Key Takeaways
- Optimal subject line: 36-50 characters for best open rates
- Mobile preview: iPhone Mail ~40, Gmail app ~37, Android 33-43, Desktop Gmail ~70
- Personalized subject lines: 30.5% higher open rates (Backlinko)
- 47% of recipients open based on subject line alone
- Word count: 6-10 words
- Mobile displays less than desktop—write mobile-first
- Use preheader text to extend your subject line
- Test different lengths and formats for your audience
Conclusion
Email subject line length directly impacts open rates, with shorter subjects consistently outperforming longer ones. Target 30-50 characters for the best balance of context and brevity, front-load your key message for mobile display, and use preheader text strategically to extend your limited space. Always test with your specific audience—what works for e-commerce may differ from B2B. Try our free letter counter → to verify your subject lines hit optimal lengths before sending your next campaign.