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Brew is the AI-native ESP. Define your brand once, ship on-brand email in minutes.
Brew is the AI-native ESP. Define your brand once, ship on-brand email in minutes.
Master email subject lines with proven formulas and 100+ examples. Learn what makes subscribers click and how to write subject lines that convert.
Your email subject line determines whether your email gets opened or ignored. With the average person receiving 100+ emails daily, you have seconds to earn that click.
This guide gives you the formulas, examples, and strategies to write subject lines that consistently get opens. No fluff—just what works.
| Device | Character Limit | Recommendation |
|---|---|---|
| Desktop | ~60 characters | 40-50 ideal |
| Mobile | ~35-40 characters | Front-load key words |
| Preview text | ~40-90 characters | Extend your message |
Rule of thumb: 30-50 characters for best performance across devices.
Pattern: "[Number] [things] to [achieve benefit]"
Examples:
Why it works: Numbers are specific, promise discrete value, and are easy to scan.
Pattern: "How to [achieve desired outcome]"
Examples:
Why it works: Promises actionable knowledge, attracts intent.
Pattern: "[Question about their challenge]?"
Examples:
Why it works: Creates engagement, feels personal.
Pattern: "[Statement that creates incomplete loop]"
Examples:
Why it works: Brain wants closure, must open to complete the loop.
Pattern: "[Name], [relevant statement]"
Examples:
Why it works: Personal attention stands out in crowded inbox.
Pattern: "[Time element] + [benefit/offer]"
Examples:
Why it works: Creates FOMO, demands immediate attention.
Pattern: "[Authority/numbers] + [outcome]"
Examples:
Why it works: Leverages credibility and popularity.
Pattern: "[Benefit achieved] in [timeframe]"
Examples:
Why it works: Leads with what they get, adds urgency with time.
Pattern: "[New/Introducing/Announcing]: [thing]"
Examples:
Why it works: News is inherently interesting, suggests value.
Pattern: "[Exactly what the email contains]"
Examples:
Why it works: Sometimes direct clarity is the best approach.
A/B testing is how you stop guessing which line wins.
| Week | Test Element | Variant A | Variant B |
|---|---|---|---|
| 1 | Personalization | With name | Without |
| 2 | Length | Short (5 words) | Long (10 words) |
| 3 | Format | Question | Statement |
| 4 | Urgency | With deadline | Without |
Looks spammy, triggers filters, feels aggressive.
Desperation isn't attractive. One exclamation max.
Opens mean nothing if content doesn't match. Destroys trust.
"Check this out" — check what? Be specific.
If they don't understand, they won't open.
"Free," "act now," "limited time" in excess can hurt deliverability.
AI can help with:
Brew generates subject lines automatically when creating emails, with options for A/B testing.
Before sending, verify:
Subject lines are the gateway to everything else. Master them and your entire email program improves.
Ready to improve your opens? Try Brew free and let AI help you write subject lines that convert.
For the rest of the email after the open, see how to write marketing emails. The US primary-purpose test sits in 16 CFR 316.3. To contact us about this article, write Brew support.
A subject line is the inbox sentence that has to match the body.
A bait subject is one that looks like a receipt or a login when the mail is a sale.
Preview text is the second sentence in many inboxes, and it should not repeat the subject.
For example, a password-reset subject on a promo is how you earn a complaint.
| Move | Why it matters |
|---|---|
| Tell the truth | CAN-SPAM still judges the subject |
| Test on a real phone | Truncation is the usual failure |
US commercial mail still follows the FTC CAN-SPAM guide and 16 CFR 316.3. Bulk sending still has to meet Gmail's sender requirements. To contact us about this article, use the support link above.
This guide's rule of thumb is 30 to 50 characters so the useful words survive desktop and mobile truncation. Desktop can show about 60 characters. Mobile often shows 35 to 40. Put the point first. Preview text, about 40 to 90 characters, should extend the message instead of repeating it.
Ten patterns cover most sends: a number of things, a how-to, a question, a curiosity gap, a name, a deadline, social proof, a benefit in a timeframe, an announcement, and a plain label of what is inside. Clarity and a specific promise beat a clever line people cannot parse.
A name can help when the rest of the line is still specific: a report, a leftover cart, an offer that is actually theirs. A name plus a vague "quick question" is just another inbox trick. Test name versus no name on your list instead of assuming it always wins.
Skip ALL CAPS, stacked exclamation points, and a subject that does not match the body. Generic phrases like "check this out" waste the open. A line so clever they cannot parse it will not get clicked. Piling on words like "free" and "act now" can also hurt deliverability.
Change one thing: length, name, emoji, tone, question versus statement, or a deadline. This guide wants 1,000 or more recipients per variant and two to four hours before you call a winner. Write down the result so the next test is not a guess.
