Characters–
How to use it
- Type or paste your subject line, merge tags included.
- Check where it's cut off in each app.
- Fix anything flagged, then try a shorter version.
Where the cut-off points come from
The phone limits are from BuzzStream's device tests published in June 2026: about 37 characters in Gmail on iPhone, 38 in Outlook on iPhone and 48 in Apple Mail on iPhone. Desktop Gmail shows more, roughly 60 to 70.
Why a fake "Re:" is flagged
Starting a new email with "Re:" pretends it's a reply. In the US, CAN-SPAM forbids deceptive subject lines, and people notice.
Questions people ask
How long should an email subject line be?
Short enough to show in full on a phone: about 37 characters fits Gmail on iPhone. Clarity matters more than a number, so cut words that add nothing.
Does this tool store my subject line?
No. It runs entirely in your browser; nothing is sent anywhere.
Should I use merge tags in subject lines?
They can help, as long as every recipient has a value or you set a fallback. An empty tag in a subject line looks broken.