Study of 2 million emails shows that 4-word subject lines have highest open rates

According to a recent study by Marketo, the best length for an email subject line is 4 words.

Marketo reviewed open rates for over 2 million emails and found that subject lines with only 4 words total receive the highest open rate (at 18.26%) than emails with 5, 6, 7, 8, 9, or more words (not including “RE:” or “FWD:”).

Why are email subject lines so short today?

Why do 4-word subject lines work so well?  Most likely, it’s because people today read emails on smaller devices.

In fact, 61.9% of all emails are now opened on a smartphone (and according to a separate study by Adobe, that number is as high as 88% for millennial readers.)

But the challenge is—iPhones only show about 41 characters in portrait mode, while newer Android phones show roughly 30 characters.

To get your message pulled out of the reader’s daily pile of emails to be answered, you’ll want to make sure that your readers can easily see the entire subject line in one glance.

Is it ever OK to use longer subject lines?

Long subject lines still work well on a desktop.  But keep in mind that as few as 9.8% of all emails today are opened on a desktop.

Also, I still occasionally stumble across audiences that respond to longer subject lines.  Experimentation is the key.  Try to learn what your audience likes—and which emails get opened more frequently.

How can you shorten your subject line?

So how do you write a short subject line?  The easiest way is to write it out first—then try to shorten it.  (And shorten it again, if necessary.)

This takes a little practice (it’s actually easier to write a longer subject line than a shorter one!).  For example, here’s how I started—then shortened—a few of my recent email subject lines.

I’ll show you the longer version, then how I edited it before clicking SEND:

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