Most people's inboxes are a complete madhouse, so getting potential customers to open your marketing email is hard. Just about every business owner knows that, and anyone with even a little experience with email marketing can rattle off the basic advice on improving your open rate: Be thoughtful about when you hit Send, personalize where appropriate, and of course, make your subject line punchy.

Great tips, all, but a business owner could legitimately ask for a little more guidance. Where exactly is the line between personal and creepy? When exactly is the ideal time to release your email out into the world? And exactly what constitutes a punchy subject line?

Controversy rages about many of these questions, but in a LinkedIn column recently, Madhu Gulati, president of ShowMeLeads, claimed to have a definite answer to that last one. She says research proves that there is a very specific word count you should be aiming for in your subject lines.

The Research

Gulati cites research that analyzed 260 million emails from 540 campaigns to determine the optimum subject-line length for a marketing email. All that data crunching, she claims, revealed clear, actionable insights for marketers:

  • Subject lines with six to 10 words generated a 21 percent open rate.
  • Subject lines with five or fewer words were opened approximately 16 percent of the time.
  • Subject lines with 11-15 words had around a 14 percent open rate. Despite this, more than half (52 percent) of the emails fell in this range.

The Takeaway

There's no mystery here--the takeaway is obviously that you should aim to keep your subject lines from six to 10 words and be aware that the most common way to go astray is to be too lengthy. Following this simple guidance seems likely to boost your open rate 5 percent or more.

That length may work because people are simply lazy or extremely pressed for time because of email overload, but Gulati also speculates that the frequency with which people check their email on their smartphones probably plays a role. "Short subject lines are optimal for mobile users, as they could easily be displayed on their mobile gadgets," she writes.

The perfect email will always be subjective to some degree, but when it comes to subject-line length, this data seems pretty clear. Why not give your subject lines the chop and see if your results mirror the ShowMeLeads results?