It’s an endless debate: Do email subject line lengths matter? At Persado, we decided to get the answer to this by testing and analyzing 20,000 email subject lines.
Our content platform, which combines natural language processing and machine learning technologies, can generate the precise words, phrases, and images to inspire any given audience to act. For subject lines, our platform optimizes for 4 key components: Formatting, Emotion, Positioning, and Description.
To categorize the subject line lengths, we separated the whole set into 4 groups based on character length frequencies. We took it one step further by running the test by industry – including financial services, telecommunications, travel, and retail – to see if certain industries saw a correlation.
In all cases, the test showed not even a moderate correlation between subject line length and performance for either click or open rates.
Bottom line? It's not about the length of your message; it's about the words. Our extensive experience shows emotional language and compelling descriptions to have the greatest effect on inspiring action. Depending on the best execution of these elements, subject line length can vary dramatically. Sometimes it might take 50 characters, sometimes 178. It’s what you say, not how long it takes to say it.