As a marketer, you work hard to write great copy and create compelling emails, but if you aren’t writing subject lines that encourage subscribers to read your messages your campaigns could fall short.

With more and more emails being opened on mobile devices, which typically show fewer characters of a subject line than a desktop, you many be wondering if your subject lines should be shorter to accommodate your on-the-go subscribers. Is there a secret to the perfect subject line length?

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. In this post, 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.

emails opened on a mobile device

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:

email subject line length

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:

most popular email client report from Campaign Monitor

Understanding that the majority of our subscribers are viewing our newsletter in Gmail and on iPhones would suggest we should optimize our subject line length to between 41 characters (portrait view on an iPhone) to 70 characters for Gmail.

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.

Email subject line length and read rate from Return Path

Here are a few email subject lines paired with their character length to give you an idea of what 65 characters looks like:

Email Subject Line Character Count Work Can Wait – These Sales are THAT Good 41 Make a Meatless Loaf Even Meat Lovers Will Love 47 Cyber Monday For Those Procrastinators 38 7 Habits That’ll Make You the Leader Your Colleagues Aspire to Be 65 5 SEO Trends for 2016 | Mobile vs. Desktop Search | Win/Loss Analysis | SMB Expectations 88

As you craft your email subject lines keep in mind where your subscribers are opening your campaigns. If the majority of the opens are happening on iPhones, you’ll want to use shorter email subject lines to get the most impact and keep your offer or CTA at the beginning of your subject line where it is most likely to be seen. You can also use preheader text to add more context to your subject lines in the preview pane.

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.

A/B test email subject line length using Campaign Monitor

Leverage email subject line best practices

Finding the ideal length for a subject line is an important step in your email marketing, but subject lines are not just about length. In order to see success, you’ll need to leverage general best practices. Remember to:

  • Use different subject lines. If you use the same subject line over and over, it won’t excite your subscribers. New subject lines encourage subscribers to open emails to see the latest and greatest.
  • Use personalization. People love the sound of their own names, so use personalization right in the subject line. You can use many other personalization options based on the data you have about your subscribers. This data can be collected through your sign up form, or from other sources like Shopify or Sauce.
  • A/B test subject lines. You’ll never know what works best without a test, so test your subject lines to find the best one.

Wrap up

At the end of the day, the best email subject line length will vary from brand to brand. That means it’s best to test out different lengths to see what works for you. If you leverage your past data and test your subject lines, you’ll be well on your way to creating email subject lines that encourage subscribers to open and take action with your campaigns. For more subject line tips, check out our 8 email subject line formulas.

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