Email Subject Line Length Checker

Your email subject line is the first thing subscribers see, and it gets truncated differently on every email client and device. Gmail mobile shows only 41 characters. Yahoo Mail mobile shows just 36 characters. If the most important part of your message gets cut off, your open rates suffer. This tool shows you exactly how your subject line appears across 12 major email clients so you can optimize it before sending.

Why subject line length matters

Research consistently shows that subject lines between 30 and 60 characters have the highest open rates. Shorter subject lines display fully on mobile devices where over 60% of emails are now opened. However, too short and you lack the context to compel a click. The sweet spot depends on your audience and content, but seeing the actual truncation points helps you make informed decisions.

Optimize for mobile first

With the majority of email opens happening on mobile, the first 35-40 characters of your subject line need to stand alone. Front-load the most important information and leave secondary details for the end. Pair your subject line with a strong preheader text that fills the preview space on clients that truncate your subject early.

Test before you send

Use this tool alongside the subject line tester which checks for spam triggers and emotional impact. Run your final subject through the spam word checker to avoid words that trigger filters. If you are A/B testing subject lines, our A/B test calculator helps you determine the right sample size for statistically significant results.

The preview text generator helps you craft the preheader that appears after your subject line in the inbox. Together, the subject line and preheader form the complete first impression your email makes.