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The best length for an email subject

Category: Email Marketing

Imagen The best length for an email sub

Your opening rate will depend on whether you're choosing a good subject line or not. The subject line is one of the most important elements of every campaign and requires all the possible attention to choose the right words. When faced with the task of writing it, the first question that you should ask yourself is: how long should it be?

To determine the best length for the subject line, look at the device from which emails are most often opened. This is the most direct answer because it varies whether a subscriber reads the newsletter from a computer or a tablet.

  • On the desktop, the screen resolution has as much influence as the email manager: it can be read in full along with the preheader, or the preheader can be cut off if the subject is too long. In the following example, we can see how both the subject line and the pre-header are cut off if they are too long:

  • On mobile, space is much more limited, so the width of the screen is affected even more: in the inbox, the subject and pre-header can only be read in full if they are about five words each. In the following example, the subject line is displayed in its entirety, but the preheader is not, as it is longer than 5 words: 



Since mobile phones have increased their presence in email statistics, subject lines have been reduced in length so as not to distort their meaning too much and not to lose opens. This is why we need to take extra care of the first words: because they will be the ones that are sure to be seen on any device.

In addition, the pre-header has also gained prominence as a differentiating element: it allows both the subject to stand out and to be better understood if it is used to extend it a little more and to behave as an additional line of the email.



Although it is possible for the subject line to be seen correctly if you write more than seven words, we recommend you not to write it that long and to not use more than 30 characters so that it does not get cut off on mobile devices. Also, if the maximum would be 50, the minimum should be 10 characters if you want it to have some strength and arouse interest.

Keep in mind that we are talking about characters. The equivalent is a very short sentence, but it will vary in length if some personalisation is used. For example, the name tag can add four more characters to the total number of characters in the case of "Luis" or double the number of characters if it is "José Luis". Keep this margin in mind to make your dynamic subjects as complete as possible.

Unfortunately, there is the possibility that the word "[SPAM]" will also appear in the subject line of the email, subtracting six characters but, above all, making it doubtful whether to open it or delete it unceremoniously. This is an accident that can happen and you can try to avoid it by keeping an eye on your wording and content, among other practices.


How to choose the length of the subject line

There are many ways to write the subject line, but this time we are going to focus only on the length. To decide which is the right one and how to make the best use of it, you need to look at the previous statistics on your list. From there you can extract details that will help you choose the ideal number of characters or length.

You have to look not only at the devices and email clients of the list, which, as we have already said, can help you to see if you can take advantage of the 20 extra characters you have if the vast majority of subscribers use a computer to consult your campaigns (remember: maximum 50 in general, but 30 on mobile).

Also review specifically how is the subject line of your email marketing campaigns that have had a higher percentage of openings, for example from the last semester. Make a table with the data and check what they have in common:

  • How many characters did you use? Find out the range in which you usually move and if it coincides with the best percentages.
  • What does your preheader look like? Consider whether you take up all the space in the subject lines and the distribution of characters between them.
  • Did you included any emojis? Is it a way to save space or maybe you use them to identify the content?
  • What kind of subject line is it? Do you always use the same style in your digital marketing or does it vary from your social media for example?
  • Do you have any personalisation tags? The most common is the name, although any other tag will do if it supports the message.

These questions can be complemented by analysing the opposite end of your results, i.e. the subjects of the campaigns with the worst opening rates. Also, never forget the targeting because it can vary from campaign to campaign, so you can also study the results of the longer and shorter ones to confirm if your conclusions are correct. For example: do the shorter ones have more conversion because they are more direct or the longer ones have more clicks because the content is better explained?

If you take all these factors into account, you will be able to better assess the length that works for you and apply it to future communications. However, it is good practice to continue experimenting with the subject line to maintain the best opening rates


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