Deliverability
Subject and preview text length tester
Count a subject line and preview text against the character cut-offs email service providers have actually measured, by client.
Free, no accountIn your browser
Counted character by character against ESP-measured cut-offs for each client.
What shows after the subject in an inbox list, before the message is opened.
Result
Enter a subject and preview text to see where each client cuts them off
Nothing to count yet. The ESP-measured cut-offs below are shown either way, with their sources.
Measured cut-offs, by client
| Client | Measured cut-off | Shown at that length | Source |
|---|---|---|---|
| Android Gmail app | ~33 characters | - | emailtooltester.com, knak.com |
| iPhone Mail | ~37 characters | - | emailtooltester.com, knak.com |
| Desktop inbox (Gmail, Outlook) | ~70-88 characters | - | emailtooltester.com, knak.com |
| Preview text (any inbox) | ~40-90 characters | - | emailtooltester.com, knak.com |
Every figure here is an ESP measurement, not a published Gmail or Apple limit.
What this is
This subject line length checker counts a subject and a preview line against character cut-offs that email service providers have measured, client by client - desktop around 70-88 characters, iPhone Mail around 37, Android’s Gmail app around 33, and a preview line around 40-90, all from emailtooltester.com and knak.com. None of these is a rule Gmail or Apple publishes, and the result says so on every run.
An inbox list shows a subject line and, next to or under it, a short preview pulled from the message - usually the opening text, unless a preheader overrides it. Every client truncates both somewhere, but where depends on the screen, the font and the client version, none of which any tool reading a typed-in string can see.
What can be measured is where that truncation tends to land on real devices, which is what emailtooltester.com and knak.com have published and this tool counts against. Treat every figure here as a measured midpoint to aim inside of, not a line a message is guaranteed to be cut at.
How to read the result
A subject past a client’s measured cut-off is shown truncated, exactly as that client would likely show it, so the actual effect is visible rather than just a character count. A subject between the lower and upper end of desktop’s range is flagged as "may" cut off, since that range exists because desktop clients disagree with each other, not because the figure is fuzzy.
The preview line is checked against one range rather than per client, because every source read for this tool reports preview-text truncation as roughly consistent across inboxes rather than split by platform the way subject lines are.
Common mistakes
What goes wrong most often, and how to tell.
- Calling 37 characters "Apple’s limit"Apple has never published an official character limit for Mail. 37 is what emailtooltester.com and knak.com have measured iPhone Mail actually show before truncating - a real number, but an ESP’s measurement, not a documented platform rule.
- Writing to the shortest cut-off and leaving the rest of the subject unusedAndroid’s ~33-character figure is the most restrictive of the three measured here, but writing every subject to fit it wastes the extra room desktop and iPhone readers would have seen. Put the part that must be read first, and let the rest trail into what gets cut on the smallest screen.
- Forgetting that a preheader overrides the preview text entirelyWithout one, most clients fall back to showing the message’s own opening line or alt text as the preview - which is rarely written to read well standing alone next to a subject.
Questions
What people ask about this tool.
- It depends which client the reader opens it in: emailtooltester.com and knak.com measure roughly 70-88 characters before desktop inboxes truncate, around 37 on iPhone Mail, and around 33 on Android’s Gmail app - the smallest of the three, and the one to write toward if a subject must read completely on every screen.
- No. Neither company publishes an official character limit for a subject line. 37 characters is an ESP measurement of where iPhone Mail tends to truncate, not a documented platform rule, and it can move with font size, screen width and client version.
- Roughly 40-90 characters is the range emailtooltester.com and knak.com measure most inboxes showing. Shorter leaves visible space unused in the list view; longer tends to be cut off before the reader sees all of it.
- Because "37 characters" is harder to picture than seeing the actual words a reader on that client would see before the rest disappears. The truncated preview next to each client’s count is what the cut-off actually looks like, not just a number.
Sources
Every fixed value here comes from the provider’s own documentation. These pages change, so each says the day it was last read.
- EmailToolTester, “Email Subject Line Length: How Long Should It Be?” read 11 October 2026
- Knak, “Email Preview Text: Best Practices and Character Limits” read 11 October 2026
Use it from the API
The same check, as one request.