How to Optimize Your Email Subject Line Length

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

More and more emails are being opened on mobile devices, which usually show fewer characters. With this in mind, you might be wondering if your subject lines should be shorter to accommodate subscribers on the go.

Is there a secret to the perfect subject line length?

Every subscriber list is different, so the ideal subject line length depends on a variety of factors. But it is possible to gain insight into the ideal lengths for your field. Open those ideas, and you’ll be bound to see increased engagement and performance from your marketing emails.

In this post, we will share some actionable tips for finding the right email subject line length for your email marketing strategy.

Factors to consider when determining email subject line length

There really is no such thing as one size fits all. In fact, the ideal subject line length depends on a variety of factors.

1. The devices and clients your emails are read on

The number of emails opened on mobile devices has increased exponentially over the past decade. In 2021, mobile phone accounted for 41.6% of all slots. However, somehow, 1 in 5 emails sent is still not mobile optimized.

While mobile optimization has to do with the code or template you’re using, it has implications for the subject line as well. Different devices will cut subject lines differently, and if you don’t test it, you could end up with some painfully embarrassing results.

Fortunately, Campaign Monitor’s inbox preview feature allows you to see your email previews in 25+ different email clients before sending out your campaign to make sure your email looks great in any inbox.

Screenshot of campaign monitor design and spam tester

When considering which subject line length will work best for marketing emails, consider using data to identify subscribers’ devices. Do most of your subscribers open emails on mobile, or are they sticking to their desktop?

Campaign Monitor users can easily find this information in your Campaign Monitor account, in the Campaign Reports section under Email client usage. This will help you improve subject line length.

Here are some stats for 2021 for the top 10 email and client devices including market share:

2021 email client data.

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Since most people see emails on iPhones and Gmail, improve the subject line length to between 41 characters (portrait width on iPhone) to 70 characters for Gmail. You don’t want a broken experiment because the subject line is too long.

2. How did the previous thread lines perform?

It’s also a good idea to look at subject lines that have had high open rates in your previous emails.

High open rates could be caused by the deals you were offering, the time of day, or because of the copy and sentiment in the subject line itself.

However, it’s worth taking a look and seeing if there are any trends that emerge from email open rates and subject line length.

So, what is the optimal length for an email subject line?

According to a study from Marketo, 41 letters, or 7 wordsSeems to be a great place for email subject line length, which is about 10 characters less than the average subject line.

Subject line length


Here are some email subject lines associated with their character length to give you an idea of ​​what a 41-character line looks like:

Email subject line

Character count

Work can wait – these sales are good 41
Make a meatless loaf that even meat lovers will love 47
Internet Monday for those procrastinators 38
7 habits that will make you the leader your colleagues aspire to be 65
5 SEO Trends for 2019 | Mobile vs desktop search | Win/Loss Analysis | SMB . forecast 88

As you craft your email subject lines, remember when and how subscribers read your emails.

If the majority of unlocks happen on iPhones, you’ll want to use shorter email subject lines to get the most impact. Additionally, keep your offer or CTA at the beginning of the subject line where it will most likely be seen. You can also use pre-title text to add more context to subject lines in the Preview pane.

Email subject line

9 email subject line best practices to take advantage of

Finding the perfect subject line length is an important step in email marketing, but subject lines aren’t just about length. In order to achieve success, you will need to take advantage of general best practices.

1. Use different subject lines

If you use the same subject line over and over again, it won’t excite your subscribers. So, instead of using our January 2021 Corporate Newsletter, try to be more creative and encourage your subscribers to open their emails and see the latest and greatest information you have to offer.

2. Keep topic lines short

Short subject lines tend to win. As discussed above, research shows that around 41 characters is the optimal subject line length. However, some marketing experts suggest continuing your search for a shorter period.

Brian Dean, founder of Backlinko, says subject lines that average less than 16 characters have much higher open rates. He attributes this to two factors.

First, emails with shorter subject lines are more likely to be delivered. Secondly, brevity creates an air of mystery.

As Dean thought, the subject line “Are you available to meet today at 11?” (38 characters) It doesn’t have quite the same effect as “Meeting at 11?” (14 characters).

In general, keep your character count low when you can. And setting character limits for people who send email to your company might also be a wise decision.

3. Test thread lines across devices and clients

As mentioned earlier, you’ll want to make sure that subject lines display correctly across devices. Sending test emails will help make sure that the subject line is well read anywhere.

4. Consider the capitalization style

While you may not think much about how to capitalize email subject lines, you should be! There are four basic styles:

  • How to Write an Email Subject Line (Sentence Case)
  • How to write an email subject line (address case)
  • How to write an email subject line (all in lowercase)

Some marketing experts, such as Val Geisler, attribute increased open rates to a personal and informal feel. In this case, you can choose sentence case or all lowercase for the subject line.

5. Use customization

Use the assign right in the subject line by including subscribers’ names. You can use many other customization options based on subscriber data. This data can be collected through your registration form, or from other sources such as Shopify or OptinMonster.

Email subject line best practices

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This is a strong subject line because it is short, asks a question, and relates to the recipient’s previous behavior. Consider doing the same with your emails.

6. A / B . test subject lines

You’ll never know what’s best without trying different options, so test your subject lines to find the best one. You can A/B test different lengths and different types of transcription to get a good idea of ​​what your email list responds to.

Email subject line format

7. Use emojis when appropriate

While the emoji debate continues, the truth is that they are here to stay. Their judicious use of subject lines can mark your emails in an inbox with seemingly endless stacked lines of text.

There are additional benefits provided by emojis. The majority of companies don’t use them, and this may contribute to a higher response rate for the emails you use. Plus, they create powerful, emotional narratives for stories, making them ideal for shorter lines of text on mobile devices.

8. Avoid spam filters

Every email that ends up in your spam folder is a missed opportunity for open conversions, clicks, and sales. That’s why, according to extensive research by Yesware, you’ll want to avoid using the following words in subject lines.

Email subject line length in 2018

There is more to avoiding spam filters than choosing words alone. (Using all caps will get you there, too.) Regardless of anything, delete the above unwanted words and phrases from the subject lines.

9. Use automation

Although this is not strictly related to subject lines, it is worth noting that using automation in your email strategy is bound to increase your engagement metrics. Even simple automation steps like a welcome flight are effective ways to get your subscriber list up while they are more engaged.

If you can turn on the timing or context of your automated email in subject lines, your results will only improve.

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At the end of the day, the best email subject line length will vary from brand to brand. This means that it is best to test different lengths to see what works best for you.

If you build on your past data and test your subject lines, you’ll be on your way to finding out how long email subject lines should take to encourage subscribers to open up and take action on your campaigns.

For more tips on writing email subject lines, check out our post on subject line best practices.

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