The ideal subject line length. Size does matter, especially in B2C.

Subject lines can have a huge effect on the response rates of your email campaigns. Adestra recently published a subject line report for which it analysed nearly a billion email marketing messages.

From this research comes the answer to the question: “What is the ideal length of a subject line?”.

How long should your subject line be?

Even if you keep the content of the email campaign exactly the same, changing the subject line can show dramatic improvements. With increases of 10%, 20% or even doubling your click troughs, subject lines are a very important part of an email. The length of the subject line is one of the influencers. Let’s see how the number of characters in the subject line corresponds with email marketing results.

the ideal subject line length

In this graph we see the deviation from the average open, click through and click to open rates grouped by number of characters in the subject line. The open rates ( the green line) have a positive spike for the very short and very long subject lines. When taking click through and click to opens into account, it seems the longer subject lines are a lot more effective, both gathering more opens and more click throughs.

Ideal subject line length per sector

It is interesting to see these results, but of course they are averages across all industries. When the subject line length were split by industry, the results shifted. For instance in the Event sector using 9 to 14 words in the subject line produced a lower than average open rate and in most cases click through rates too. While in Publishing, these were not nearly as negative with subject lines in that range even doing better than average.

This again shows that you cannot take general statistics and translate the directly to any list or sender.

B2B versus B2C

There are huge differences in the way B2B and B2C email programs are run. Of course because of the distinction between business and consumer orientated email. This also shows through in the B2B subject line length and their B2C counterparts.

Subject line length in the B2B sector

In B2B emails, longer subject lines work better than shorter subject lines. Also when looking at the number of words. Subject lines with 6 – 10 words will drive open rates, but don’t deliver the click throughs. In the report 6 -1 word subject lines are advised for awareness emails that don’t necessarily have a direct need for a call to action to click.

After 130 characters, there is a drop of the open rates, but also a huge increase in the number of click throughs. Anything over 16 words can deliver on both opens and clicks.

B2C subject line length shows mind-blowing results

The differences in B2C are much bigger than in B2B. Subject lines with 3-5 words appear to have a very bad effect on open and click through rates. Subject lines with 3 or 4 words preform around 40% worse than average both in open rate and in clicks.

The subject lines with over 80 characters do hugely better in B2C email marketing. It seems to be that making your subject line stand out, is ever important. A long subject line can do just that in B2C, with the added information and length to account for higher open and click through rates. A 20 word subject line appears to be the real champion in this research, with a 115% uplift in opens and 85% uplift in clicks.

Testing Subject lines purely on length

Of course subject lines or subject line length  isn’t all you should be looking at. And even if you wanted, there is no way to do a subject line test purely on length. Because adding more words / characters also changing other elements of the subject line. All elements of a subject line can affect the amount of interest in your campaigns. Testing can be a part of your email marketing strategy. See the video on how to  Optimize subject line force with this 4 step checklist  from an earlier blogpost.

Update: New data by Mailchimp

Hey, a little update! Mailchimp just posted some of their data in an excellent blogpost by John Foreman. One of the interesting things in there is that they found that for a lot of their clients (something over 6 billion of the 12 billion, a bit more than 50% of their data) the subject line lenght shows no correlation with open and click results. You have to wonder what it means about the other 50% though…. Anyway, Interesting stuff!

So what I advise you to do, if you really want to know about subject line length. First read this article (not skim, read. Sheesh!). Then head over to the article by John and read, not skim that too.

Reading what is actually in both articles will make a lot more sense than just running through the headlines and looking at the pictures.
And then – if you are ready to test your subject lines, and still interested in subject line length – read this article about how to do better email split tests and answer the questions there. If you have any additional questions (I hope so), please post them in the comments.

Jordie van Rijn

Jordie van Rijn is an independent email marketing consultant. He specializes in smart email marketing, event-driven campaigns and email tool selection. As a consultant, Jordie will help you get the most out of your email marketing efforts.