The best number of words in an email subject line

On the Marketo blog, they’ve been looking at the optimum number of words in an email subject line. The research covered 200 campaigns containing over 2 million emails. I’ve seen this done before, but times change, so new analysis is always worthwhile. They didn’t just look at email open rate, because in the end, it’s all about the recipient taking action. An intriguing but misleading subject line could get a great open rate but a low number of subsequent actions (normally click-throughs to somewhere).

The highest open rates occurred with short subject lines and the lowest with long subject lines. But the ‘click-to-open’ rates didn’t correlate. The author suggests that “more people might click an email with a nine-word subject line because they had a better sense of the email’s content from the start.”

Once overall engagement was factored in, the winner was seven words. It looks to me like six or seven words is our best bet. See what you think.