Open rate. Click-through rate. Ask most marketing teams how their email program is performing, and these are the numbers they’ll show you.
But here’s the thing: Open and click metrics don’t tell you if your email program is actually working. They tell you how people interacted with the email message, not whether the email generated meaningful results for the business.
Relying on them as key performance indicators (KPIs) can lead to completely wrong optimization.
What open and click rate data shows
I’ve seen subject line A/B split tests where the version with the highest open rate produced fewer conversions or lower revenue per email (RPE) than other versions. I’ve also seen campaigns where the version with the highest click-through rate generated fewer conversions or a lower RPE than other versions.
This is not just anecdotal. Looking at the subject line tests I’ve conducted for a wide range of clients and audiences over many years, the results are striking.
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Open rate as a KPI: Rarely useful
Many marketing teams use open rate as their primary KPI for subject line testing. After all, the subject line determines whether someone opens the email. But if your business goal is about conversions or revenue, open rate is a weak indicator.
In the subject line A/B tests I conducted using the scientific methodI came back to see how often the highest open rate was a correct predictor of the version with the highest conversion rate (for non-profit stocks) or RPE.
Data suggests that if your marketing department relies on open rate as a KPI for your subject line testing:
- In 20% of cases, your results will correctly identify the version with the highest conversion rate or RPE.
- 10% of the time, your results will not correctly identify the highest converting RPR version.
- In 70% of cases, the variance in your open rate will be within the margin of error and therefore inconclusive, even if there is a clear version with the highest conversion rate or RPE.
The open rate misled the analysis or provided no useful information in 80% of tests.
Click-through rate is even worse
If the open rate is not a reliable KPI, some turn instead to the click-through rate. This seems reasonable: clicks occur later in the funnel, so they should correlate more closely with conversions or revenue.
Unfortunately, the data suggests otherwise. When testing campaigns comparing CTR to conversion rate or revenue per email, my analysis results looked like this:
In this case:
- Just 7% of the time, the highest CTR version also produced the highest conversion rate or RPE.
- In 36% of cases, the CTR indicated the wrong winner.
- In 57% of cases, the CTR differences were not statistically significant, even though the business metrics clearly were.
CTR was only a reliable indicator of the true winner in 7% of cases.
The Metrics That Really Measure Email Performance
Diagnostic metrics like opens and clicks do not reliably predict business results. If you want to accurately evaluate email performance, you need to look at metrics that measure actual results.
Two of the most important are conversion rate and revenue per email.
Conversion rate: the metric that shows whether email is working
Conversion rate measures the percentage of recipients who take the action your email was designed to do. A conversion doesn’t have to be a sale. This could be a purchase, demo request, webinar registration, lead generation form, app download, or subscription renewal.
Here is the formula:
- Conversion rate = Conversions ÷ (Number of emails sent – Bounces)
- Multiply by 100 to express it as a percentage.
Conversion rate directly measures whether your email campaign achieves its goal. It answers the most important question: Did the email cause the desired behavior?
This is why conversion rate is often the best KPI for campaigns designed to drive action rather than immediate revenue.
Revenue per Email: The Metric That Proves Email ROI
For e-commerce programs, the metric I care about most is RPE.
- Revenue per email = Total revenue ÷ (Number of emails sent – Bounces)
- We present this measure as a dollar figure.
Unlike clicks or opens, this metric directly links email performance to financial results. It often reveals information that engagement metrics hide.
For example, I once spoke with a company that sells high-end audio equipment. They had an aggressive A/B testing program and ran a test on whether to include product prices in their email. They used click-through rate as a KPI. Here are the results.
The version without pricing generated significantly more clicks, so it was declared the winner. But think about what’s happening here. High-end audio equipment is expensive. Many recipients probably clicked just to find out the price. If the price had been included in the email, as was the case in the control version, these recipients would not have needed to click.
The higher CTR version may have simply generated more curiosity clicks, not more qualified buyer clicks. Since the company didn’t track email conversions or revenue, it couldn’t determine which version was actually generating the most sales.
Without this data, the test winner is questionable at best.
The Real Lesson for Email Marketers
Open rates and click-through rates are not useless. These are valuable diagnostic metrics that help you understand how recipients interact with your email content.
But they shouldn’t be the main KPIs of most email programs. If your goal is conversions or revenue, and most businesses are, your performance metrics should directly measure those results.
This means focusing on:
- Conversion rate to measure whether your campaigns are generating the desired action.
- Email revenue to measure the financial impact of your program.
Because ultimately, it’s not the opens and clicks that make a campaign successful, but the results.
Author’s note: AI tools were used to assist in the writing and editing of portions of this article. Test data, analysis and conclusions are based on subject line and campaign testing conducted for clients’ email programs over several years.
