How long should your subject line be & the “Wolowitz Formula”

As I stated in the video, there have been several studies conducted to answer this question.

Mailer Mailer

Mailer Mailer published the Email Marketing Metrics Report in October 2014. They researched 60,000 campaigns. Here is what they have to say:

  • Subject lines with 4 to 15 characters, earned the highest open rate (16.8%)
  • The lowest open rate (10.7%) occurred with subject lines between 40 and 50 characters

Mailer Mailer subject line stats

Retention Science

Retention Science conducted a research of 260 million delivered emails, and this is the conclusion:

  • 6 to 10 words perform best with a 21% open rate
  • Despite the fact that the majority of emails sent (52%) had a word count of between 11 and 15

Retention Science subject line stats


And Mailchimp, after analyzing 12 billion emails sent, came to say that “Subject Line Length Means Absolutely Nothing.”

Mailchimp email subject line stats

Most people will tell you that short is better.

In fact, one of the most successful subject lines in history was a simple “Hey” from the Obama re-election campaign we mentioned earlier in this course.


But, again, the power of this email is not really on the subject line but on the “from name.” We’ll talk about that soon.

Other considerations

When writing a subject line, there are other things to consider that affect the length, but are probably more important:

1) Message

The content of the message is more important and can have a bigger impact than the length. If you prioritize the length over the content, you might end up with a poor message.

2) Limit

You have to consider the character limit on different email clients. Having your subject line cut off is never a good thing.

This is why it’s important to preview your email subject lines in different email clients. There are 2 ways you can do this:

2.1) Use an email preview service like Litmus or Email on Acid

Email on Acid

2.2) Have an email account on the main clients and test your campaign before sending them.

You also have to do this with mobile, since the character limit is usually shorter.

3) Pre-header

The longer the subject line, the shorter the pre-header text. We have a lesson dedicated to pre-header text later in this module.

The “Wolowitz Formula”

This is a screenshot of my inbox showing how the length of the subject lines are all within the same parameters. As you can see, only one email breaks the pattern.

The Wolowitz Formula

And this is Howard wearing his eye patch on the episode of The Big Bang Theory.

Wolowitz eye patch


Your homework in this is simple:

On your next campaign, run an A/B Test with 2 variants:

  • A regular subject line
  • A subject line that is either shorter or longer than usual

Of course, always prioritizing the quality of the message you want to communicate.

See you on the next lesson!