Subject Line Length Checker: Will Your Subject Get Cut Off?

Your subject line has one job: earn the open. But if it runs too long, the inbox cuts it off, and your best words never get read. This checker counts the characters and words in your subject line and shows a mobile inbox preview, flagging the moment your subject crosses the length where phones start truncating it.

How long should an email subject line be

There is no single perfect length, but there is a clear danger zone. Phones, which now account for most email opens, typically show only around 40 characters of a subject line before cutting it off. Desktop clients show more, often 60 characters or so, but you cannot count on your reader being at a desk.

The practical rule is to aim for roughly 40 characters or fewer when you can, and to keep the most important words at the very start. This checker marks subjects up to 40 characters as safe, warns between 40 and 60, and flags anything longer as likely to be trimmed on mobile.

Front-load the words that matter

Because the end of a long subject can vanish, the safest habit is to lead with the words that make someone want to open. Put the offer, the benefit or the urgency first, and save any softer words for the end where truncation does the least damage.

The mobile preview above shows you the first 40 characters, which is roughly what a phone displays. If the visible part still makes sense and still tempts a click on its own, your subject will work even when the tail is cut. If the meaning only lands once you read the whole thing, shorten it.

Length is a constraint, not the whole game

A short subject that says nothing will not beat a slightly longer one that promises something real. Length is a boundary to respect, not a target to chase. Within that boundary, clarity, curiosity and relevance are what actually move the open rate.

Check the length here, then judge the words themselves against your audience. Strong subjects lift opens, but opens only pay off when the list is full of the right people. If you want to grow that list through search, request a free audit and we will show you where the readers are.