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Email Subject Line Length Checker
Tool details
Count the characters in an email subject line and see whether mobile inboxes are likely to cut it. Aim for about 40–60 characters and put the key words first.
Your subject line
51
Good for most inboxes
Approximate mobile preview
Your Q4 webinar seat is confirmed: see y…
Cut at 40 characters as a rough guide. Real clients vary by device and font.
How to use the subject line checker
Paste the subject, read the count and band, then shorten from the end so the offer, action or date stays at the front. Preview important sends in your own mail client, tag the links inside with the UTM link builder, and make sure the message reaches the inbox with the email deliverability checker.
What the bands mean
- 40 or fewer: short; usually shown in full, with room for a brand or preheader.
- 41–60: fits most inboxes; check that the key words are in the first 40.
- Over 60: likely to be cut on mobile; trim or move the key words forward.
Frequently asked questions
It treats about 40–60 characters as a practical window for many mobile inboxes: 40 or fewer is short, 41–60 is good for most inboxes, and over 60 is flagged as likely to be cut on mobile. That band is a heuristic for this tool, not a universal rule.
No. Character count is a simple proxy. Wide characters, emoji and each mail client’s layout still change what fits. Use the count as a first pass, then preview in your mail client when the send matters.
Not always. Transactional subjects can be shorter, and some brands prefer longer subjects for desktop-heavy lists. Treat the band as a default for campaign email, then adjust from your own open and click data.
At the front. If a mobile inbox cuts the subject, the first 30–40 characters are what people see, so lead with the offer, the action or the date.
Subject length affects whether a delivered message gets opened. Whether it lands in the inbox at all depends on authentication and reputation, so check SPF, DKIM and DMARC with the email deliverability checker as well.