Messaging · Email
Email subject line length checker.
Count a subject in characters and bytes and see how it fits the line limits in the email standard, including when it is encoded for non-ASCII text.
Inputs
Subject length
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How long can an email subject line be?
The email standard does not set a limit on the subject itself. RFC 5322 limits each line of a message: a line must be no more than 998 characters and should be no more than 78 characters, not counting the line break. A header such as Subject: ... can be folded onto several lines, so a longer subject is allowed; the 78 and 998 apply to every line. This tool counts the header line as Subject: (9 characters) plus your text.
Non-ASCII subjects. A subject with accents, symbols or emoji has to be encoded. RFC 2047 defines encoded words of the form =?UTF-8?B?...?=, each at most 75 characters long including the delimiters. With base64 that leaves room for 45 bytes of text per word, and a multibyte character is not split across words. The tool shows how many encoded words your subject needs and the resulting header length.
What about the ideal subject length? Advice such as 40 to 60 characters is a marketing guideline and varies by mail app, screen width and font. No standard defines a visible cut-off, so this page gives the standard’s limits and your exact count, and leaves the display choice to you.
Worked example. A 69-character ASCII subject makes a 78-character header line (9 + 69), which just fits the recommended line length; a 70-character subject makes 79 and would be folded onto a second line. A subject like Café menu (9 characters, 10 UTF-8 bytes) becomes one encoded word of 12 + 16 = 28 characters.
Frequently asked questions
What is the maximum length of an email subject line?
RFC 5322 says each header line must be no more than 998 characters and should be no more than 78. A longer subject can be folded across lines, so there is no single limit on the subject itself.
How many characters should a subject line be?
No standard sets an ideal length. Mail apps truncate by screen width, so shorter subjects are safer on phones, but the exact cut-off varies by app and device.
Do emoji count against the limit?
They are encoded. An emoji is 4 UTF-8 bytes, and the whole non-ASCII subject is turned into RFC 2047 encoded words, which makes the header line longer than the visible text.
What is an RFC 2047 encoded word?
A way to carry non-ASCII text in a header, written =?UTF-8?B?...?=, at most 75 characters long. Long subjects are split into several encoded words.
Is my subject line sent anywhere?
No. It is counted in your browser.
Sources
Checked
RFC 5322 section 2.1.1 gives the 998 (MUST NOT exceed) and 78 (SHOULD NOT exceed) per-line limits. RFC 2047 gives the 75-character encoded-word limit. The 45 bytes per word is arithmetic from that limit for UTF-8 base64 words. Visible subject cut-offs in mail apps are not standardised and are not given. Runs entirely in your browser.
Scope
This checks the message format, not deliverability or spam filtering. Real mail systems may fold, encode or truncate differently.