Does Subject Line Length Affect Open Rate? [EMAIL DATA]

Henry O'Loughlin

by Henry O'Loughlin • 1 minute read

Does Subject Line Length Affect Open Rate? [EMAIL DATA]

I had a hunch that subject line length affected open rate. My thought was that the shorter the subject line was, the higher the email open rate would be. Essentially, less is more.

But I took a look at a little over a half of a million emails from Nectafy and our clients, and I found that, surprisingly, subject line length doesn’t really impact open rate at all.

I’ll take you through my findings and offer some takeaways on what makes a good subject line.

Here’s where the data comes from:

  • Three HubSpot portals (Nectafy’s and two clients’). These include two types of messages:
    • Published Emails: Bulk emails to a list on the database (i.e., a newsletter or blog roundup email).
    • Automated Emails: Nurturing email series that are sent out based on an action the lead has taken on the website.
  • 519 individual messages sent.
  • 579,169 total emails delivered.
  • 165,054 total emails opened.

Email metrics for the data set:

  • Delivery rate: 98.8%.
  • Open rate: 28.5%.
  • Click through rate: 8.4%.

Does subject line length affect email open rates?

If we’re truly looking for a statistically significant answer, there is no correlation between subject line length and open rate based on the data set I worked with. Return Path also looked at this theory for a much larger data set and didn’t find a correlation.

If you look at the charts below, your mind might trick you into seeing a slight downward trend as your subject length increases. Don’t trust it!

Here is a comparison between the number of words in the subject line and the open rate:

Does Subject Line Length Affect Open Rate? [EMAIL DATA]

Here is a comparison between the number of characters in the subject line and the open rate:

Does Subject Line Length Affect Open Rate? [EMAIL DATA]

Takeaway: Subject line length doesn’t correlate with open rate. Therefore, the quality of the message, the sender name, and email address would likely have the biggest impact.

(You’ll notice that this contradicts a conclusion I reached back in early 2015. I would defer to this data set since it is much bigger and includes a few different industries.)

Do automated or bulk emails perform better?

The next theory I looked at was whether or not the type of email impacted performance.

  • We send either bulk emails (called “published” emails in HubSpot) to big lists of people at certain times.
  • We also send automated emails to individuals based on an action they took on the site.

Here is a comparison of those two types of emails:

Does Subject Line Length Affect Open Rate? [EMAIL DATA]

Takeaway: As you can see, automated emails perform much better than bulk (or published) emails for both open rate and click through rate (CTR). The takeaway is simple: Automated emails get sent to an individual person based on the action he or she takes on our site. Bulk emails get crafted for a list of people.

It is easier to predict what one person is looking for than it is to predict what a thousand people are looking for.

Wherever you can, try to automate your emails based on a person’s action. Assembling lists based on certain criteria takes more work and the results are worse.

See Also: Our Secret Formula For Actually Getting Email Responses

Which subject lines have the best email open rates?

So, if open rates aren’t impacted by the subject line length, what are some characteristics of high-performing subject lines?

Here are some examples of top open rates:

  • “5 billion connections by 2022?” (72% open rate, automated email).
  • “Too expensive” (61% open rate, automated email).
  • “Would you give me your opinion about this paper I'm writing?” (60% open rate, automated email).
  • “[First Name], here’s where we keep our resources.” (60% open rate, automated email).
  • “Why I’ve had enough of HubSpot.” (54% open rate, published email).
  • “I sincerely apologize…” (53% open rate, published email).
  • “Are you ready to create your scorecard?” (52% open rate, automated email).


Based on the handful of high-performing emails above, here are my recommendations to try for your next subject line:

  • Stats and numbers work.
  • Asking for people’s opinions always works well.
  • Including the first name token in the subject line still works.
  • Controversy sells, so tell people why you’ve had enough of something.
  • Apologize! Let’s face it–people love seeing others mess up.
  • Ask a targeted question.

Where do we go from here?

I still have a hunch that if you craft subject lines like you’re writing to a friend rather than writing a headline, you’ll be much better off. What I mean by that is I’d always go with a subject line like “Meeting” rather than “7 Reasons To Meet With An Inbound Expert At Nectafy.”

Beyond that, though, simply focus on getting one person to open the email rather than 1,000, and you’ll find your open rates go up. Let me know what you’ve seen work with subject lines at henryoloughlin on Twitter.

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