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How long should an email subject line be? Every inbox measured
Inboxes cut a subject line by screen width, not by a character count, so the answer depends on where it’s read. By our measurements, Gmail on an Android phone shows about 33 characters, Gmail on an iPhone about 37, Apple Mail on an iPhone about 48, Outlook on the web about 51 and Gmail on a desktop about 88. If the first 33 characters make sense on their own, the subject works everywhere.
No mail provider publishes these numbers. They are Truncly’s own measurements of each inbox’s font and width, so treat them as approximate. The rules that do have official sources, the email standard1 and the preview settings in Apple Mail2 and Outlook3, are cited where they come up.
How many characters show, inbox by inbox
| Inbox | Subject shown (approx.) | Device we measured |
|---|---|---|
| Gmail app, Android | ~33 characters | Pixel 7 |
| Gmail app, iPhone | ~37 characters | iPhone 14 |
| Apple Mail, iPhone | ~48 characters | iPhone 14 |
| Outlook on the web | ~51 characters | 1,400px window |
| Gmail on the web | ~88 characters | 1,400px window |
All figures are Truncly measurements, not provider limits.
Why “approximately”? Each inbox draws the subject in its own font at a fixed width. Wide letters (W, M, capitals) use far more room than narrow ones (i, l, t), so two subjects with the same number of characters can be cut in different places. A subject in ALL CAPS can lose a third of its visible length.
The technical maximum
The email standard, RFC 5322, says each header line must be no more than 998 characters and should be no more than 781. Long subjects can be folded across several lines inside the message, so in practice the limit you’ll hit is the inbox’s width, not the standard.
Preview text (preheader)
Most inboxes show a line of the email’s opening text next to or under the subject. You can control it with a hidden preheader at the top of the email.
| Inbox | Preview shown (approx.) |
|---|---|
| Apple Mail, iPhone | 2 lines, ~99 characters (up to 5 if set)2 |
| Gmail app, Android | 1 line, ~37 characters |
| Gmail on the web | Whatever room the subject leaves on the line |
| Outlook (classic) | Off, or 1 to 3 lines, as the reader chooses3 |
Apple Mail on iPhone shows two lines of preview by default, and people can choose up to five in Settings > Mail > Preview2. Classic Outlook lets people turn message previews off or pick one, two or three lines3. The character counts in the table are our measurements.
On Gmail’s desktop inbox, subject and preview share one line, so a long subject pushes the preview off the screen. A short subject buys you more preview.
Writing to these limits
These are our suggestions, not provider rules:
- Put the point first. “50% off ends tonight: spring sale” survives a 33-character cut; “Our spring sale is here and 50% off ends tonight” doesn’t.
- Don’t repeat the subject in the preheader. It’s your second line; use it for the detail.
- Watch your sender name. On phones the sender sits above the subject, so it doesn’t eat subject space, but a long sender name can still be cut.
- Avoid ALL CAPS and emoji at the start. Both take extra width; an emoji is usually drawn wider than a letter.
- Check personalised subjects with your longest values. “Hi Alexandria,” uses twice the room of “Hi Al,”.
You can paste a subject line into our free subject line checker to see where each inbox cuts it.
Sources and credits
On-screen character figures are Truncly’s measurements, taken in September 2026. Standards and settings were read on 6 November 2026. Gmail and Android are trademarks of Google LLC; Apple, iPhone and Apple Mail are trademarks of Apple Inc.; Outlook is a trademark of Microsoft Corporation. Truncly isn’t affiliated with or endorsed by any of them.
Footnotes
-
RFC Editor, RFC 5322: Internet Message Format, section 2.1.1. 998-character limit and 78-character recommendation for header lines. ↩ ↩2
-
Apple Support, iPhone User Guide: Read email in Mail. Preview shows two lines by default; up to five can be chosen. ↩ ↩2 ↩3
-
Microsoft Support, Turn message preview on or off. Off, 1, 2 or 3 lines. ↩ ↩2 ↩3
Quick answers
What is the ideal email subject line length?
Put the point in the first 33 characters or so. That is about what Gmail on a Pixel 7 shows, the tightest common inbox we measure. Longer subjects are fine as long as the start works alone.
Is there a maximum length for an email subject line?
The email standard (RFC 5322) caps any header line at 998 characters and recommends 78. Inboxes cut the subject on screen long before that.
How many characters of a subject line show on iPhone?
About 48 characters in Apple Mail on an iPhone 14 and about 37 in the Gmail app on the same phone, by our measurements.
How much preview text shows in Apple Mail?
Two lines by default. People can choose up to five lines in Settings > Mail > Preview (Apple, iPhone User Guide). On an iPhone 14 two lines hold about 99 characters by our measurements.