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Open Rates

The ideal email subject line length: data from 10 million emails

ab_test_adam

We aggregated data from 10 million emails across our community to determine the optimal subject line length.

The data

  • 1-20 characters: 26.1% average open rate
  • 21-40 characters: 24.3% average open rate
  • 41-60 characters: 22.8% average open rate
  • 61-80 characters: 21.2% average open rate
  • 81+ characters: 19.4% average open rate

The takeaway

Shorter is generally better, with the sweet spot being 20-40 characters. But context matters: B2B audiences tolerate longer, more descriptive subject lines better than B2C.

Mobile optimization is the primary driver — most mobile clients truncate at around 35-40 characters. If your audience is primarily mobile (check your analytics), optimize for that limit.

#subject-lines#length#data
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3 Comments

copywriter_chrisEmail Copywriter

Mobile truncation is the key factor. Most of our audience opens on mobile so we aim for under 35 characters. Shorter subject lines also feel more personal.

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newsletter_nerdNewsletter Creator

Interesting data. My newsletter subjects are typically 40-50 characters and perform well. Might try testing shorter ones.

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growth_graceGrowth Marketer

We A/B test short vs long subjects regularly. For promotional emails, shorter wins. For educational content, slightly longer descriptive subjects perform better.

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