There is no such thing as the ideal length for an email subject line

‘The shorter the better’ would seem to be the ground rule for subject lines. So does this mean there’s a link between the number of characters in the subject line and the open rate in email marketing? Several studies cast doubt on this theory.

There’s no shortage of advice on Google. ‘Go for 28 to 39 characters’, ‘Keep it between 6 to 10 words’, ‘Never surpass 50 characters’. It seems like everyone has an opinion on how long a subject line should be.

Only logical, really. After all, the subject line of an email actually is quite important. Compare it to the opening line of someone you meet in a pub who is interested in you. Is that line followed by a stimulating conversation or does it turn you off?

Still, the theories on fixed subject line length are far from undisputed. Longer subject lines are not necessarily less successful than shorter ones, nor are they more successful. So what is the deal here?


The number of characters has no impact

MailChimp put the theory to the test and analysed a total of 12 billion sent emails. The length of the subject line was compared to the open and click-through rates. The result? There’s no statistically relevant correlation there.

ReturnPath performed the same exercise with 2 million sent emails. They, too, could find no connection between the number of characters and the read rate (i.e. the number of emails marked as ‘read’).

Phrasee criticised the methodology used in studies on subject line length and subsequently demonstrated how such analyses should be performed. Still, they reached the same conclusion: there is no statistical connection.

What does that mean for your own subject lines?

As MailChimp indicated: there just isn’t a one-size-fits-all rule. In your particular case, short subject lines may do just fine. Or longer subject lines may do better on average. Or perhaps it just varies from one day to the next.

Do you suspect that a longer subject line would catch on better in a specific case? Then by all means, use it, but be sure to test it against shorter subject lines that essentially deliver the same message. In case of a newsletter with multiple items it’s useful to determine whether multiple topics in the subject line – separated by a comma, for instance – would be more effective.

In other words, while there is no such thing as the sweet spot for the number of characters in a subject line, you still may have a personal sweet spot.


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