Does subject line length matter? My strategy for crafting emails that get opened

 Does subject line length matter? Does urgency matter? Does anything really matter!?

All jokes (and existential crises) aside, it all matters. The real question is how much it matters, and that depends entirely on testing. A/B testing is the key to discovering what resonates with your specific audience.

At Criquet Shirts, our target audience is 35–65-year-old dads. That audience will respond much differently than, say, teenage girls. This difference is exactly why you can’t definitively say one strategy works across the board.

Getting started with testing

Approaching testing for the first time can feel daunting. Where do you even start?

Klaviyo’s AI does a great job suggesting the types of tests you might consider running (as shown in the screenshot below). If you’ve uploaded your brand guide to Klaviyo’s brand voice settings (Content > Images & brand > Brand > Voice) you can ensure that the AI’s recommendations align with your tone and style.

These are four great suggestions to start with. I’ve also tested adding urgency (“Only a few left! Get yours now!”) and comparing generic vs. product-specific subject lines (“Check out the new Classic Players Shirt” vs. “Check out the newest polo from Criquet”).

For this example, let’s focus on length. Choose the number of words or characters you want to test for each version. I recommend doubling the word count so there’s a clear difference, for example, 3 words vs. 6+ words or 4 words vs. 8+ words.

Setting up the test

Klaviyo makes setting up A/B tests easy. Once you’ve added the second version with the alternate subject line, decide how to structure your test.

Do you want to:

• Send each subject line to 50% of your list?

• Or test with 20% and send the winning version to the remaining 80%?

For me, this comes down to list size. If you have a smaller list, it’s harder to get definitive results with only 20% of that list. Also, if you’re going to run similar length tests, you can do multiple 20% tests to get to that higher level of trust in the results.

Interpreting the results

So, you’ve run the test. What’s next?

As marketers, we love definitive results. If an open rate is 10% higher with longer subject lines, that’s amazing! But what if it’s not that clear?

In one of our tests, we looked at unique opens across nearly 400,000 delivered emails, and the results were almost perfectly 50/50.

Did that discourage me? Not at all. It encouraged me. To me, this means both styles work and that we should continue using a strong mix of both short and long subject lines.

So… Does subject line length matter?

Well, not exactly, at least not universally. The answer will come from your own testing, with your own audience, for your own brand.

What I hope I’ve done is give you the tools and confidence to find that answer for yourself.