E-mail Tips>> The Ideal Email Subject Line Length

Time:2017-03-22


Every business and subscriber list is different, so the perfect subject line length depends on a variety of factors. It is possible, however, to get some intel into what length will work best for your campaigns. And here we’ll share some actionable insights on how to determine the optimal length for yours.


Factors to consider in your email subject line length

There’s really no such thing as a one-size-fits-all length that will suit everyone. In fact, the ideal length of your subject line depends on a variety of factors.


1. What devices and clients your emails are read on

From 2010 to 2015, email opens on mobile devices increased by 30%. In 2015, more than 53% of emails were opened on a mobile device.

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It’s also important to keep in mind that your subscribers use a variety of different browsers and email clients. This further contributes to the complexity of having a one-size-fits-all optimal subject line length. This chart shows the number of characters that display across common devices and clients:

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When considering the email subject line length that will work best for your campaigns, it’s worth it to look at some data to understand which clients and devices your subscribers are using. Are most of your subscribers opening emails on mobile, or are they sticking to their desktop? This information will help you optimize your subject line length.

You can easily find this information in your Campaign Monitor account, in the Campaign Reports section under Email Client Usage. Here’s an example from our Newsletter subscriber list:


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2. Past email subject line performance



It’s also a good idea to look at which subject lines have garnered high open rates in the emails you have sent in the past.

High open rates can occur because of deals you were offering, the time of day, or the copy and sentiment in the subject line itself. Still, it’s worthwhile to take a look and see if any trends emerge from your email open rates and the length of the subject line that was used.
How many characters are optimal?

According to data from Return Path, 65 characters seems to be a sweet spot for email subject lines, which is about 15 characters more than the average subject line. When subject lines are 61-70 characters long, they tend to get read. However, most email subject lines are between 41 and 50 characters.

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Testing your email subject lines

Your email subject line is one of the single easiest elements to test in your email campaign. Tests can help you see how your email subject lines will look across devices, as well as how they compare to shorter or longer versions.


  • Send test emails to see how subject lines render on all devices. This will help ensure that your subject line reads well wherever it’s sent. Our Inbox Preview feature enables you to see previews of your email in over 25 different email clients before sending your campaign to ensure your email looks great in any inbox.

  • A/B test two different lengths. Some email service providers like Campaign Monitor, allow you to A/B test two different subject lines to see how they perform. Try testing a short and long version to see which performs better.