Email marketing remains one of the most effective channels for businesses, but tracking every metric available can lead to data overload. Not all metrics are created equal. Some are mere “vanity metrics”—numbers that look impressive but offer little strategic value.
Instead, marketers should focus on a core set of key performance indicators (KPIs) that directly impact engagement, conversions, and revenue. Email marketing can generate over $10 billion (with a “B”) in revenue, with an average return on investment of about $36 for every $1 spent (3600% ROI). Given this potential, it’s crucial to concentrate on the KPIs that truly matter for your email campaigns.
Essential Email Marketing KPIs
Deliverability Rate (Bounce Rate)
Deliverability rate measures the percentage of emails that successfully reach subscribers’ inboxes. It is essentially the inverse of the bounce rate (emails that could not be delivered).
It’s calculated as (Number of bounced emails / Number of emails sent) × 100%.
A good bounce rate is under 2%, which means you’re achieving about 98% deliverability. This KPI matters because if emails aren’t delivered, they can’t be opened or clicked. High bounce rates can harm your sender reputation and skew your other metrics (since undelivered emails aren’t giving you any engagement data). Keeping your list clean by removing invalid addresses (especially those that “hard bounce”) is essential to maintain a healthy deliverability rate.
Open Rate
Open rate is the percentage of delivered emails that recipients opened.
It’s calculated as (Emails opened / Emails delivered) × 100%.
Historically, an open rate of around 20% to 40% was considered a good benchmark, indicating effective subject lines and send times. However, due to privacy changes, this metric has become less reliable. Apple’s Mail Privacy Protection (MPP), introduced in 2021, automatically pre-loads email content (including tracking pixels) even if the user doesn’t actually open the email. This causes inflated open rate numbers.
In other words, your reports might show sky-high opens that aren’t reflecting real engagement. While you should still monitor open rate trends (e.g., sudden drops or increases), don’t rely on open rate alone to judge success. Instead, use it alongside other engagement metrics (like clicks and conversions) and pay more attention to the direction of your open rate over time rather than the absolute percentage.
Click-Through Rate (CTR)
Click-through rate (CTR) is the percentage of email recipients who clicked at least one link in your email.
It’s calculated as (Number of clicks / Number of emails delivered) × 100%.
CTR shows how engaging your email content and call-to-action are, since it measures the step beyond just opening. On average, email campaigns see around a 2% overall CTR, and marketing-specific emails average about 1.8% CTR. If your CTR is higher, that’s a strong sign your content resonated. If it’s lower, you may need to work on more compelling content or clearer calls-to-action.
To improve CTR, ensure your email copy is relevant and your buttons or links stand out with an enticing offer. Also, remember that CTR is influenced by open rate to an extent. If nobody opens the email, they can’t click. So a good subject line (to drive opens) paired with engaging content (to drive clicks) works hand-in-hand to boost CTR.
Conversion Rate
Conversion rate is the percentage of email recipients who took the desired action after clicking through your email. “Conversion” can mean making a purchase, signing up for an event, filling out a form, or any goal you set for the campaign.
It’s calculated as (Number of people who completed the goal action / Number of emails delivered) × 100%.
This is one of the most critical KPIs because it directly ties your email to tangible results. Average email conversion rates are typically a few percent; for example, automated emails can see roughly 1% to 5% conversion rates on average (some high-performing campaigns achieve even higher).
If your conversion rate is low, consider optimizing the landing page your email links to, aligning your email content better with the offer, or segmenting your audience so the right people get the right message. Even small lifts in conversion rate can significantly boost your return on email marketing, since this metric translates directly into revenue or goal completions.
Unsubscribe Rate
Unsubscribe rate is the percentage of recipients who opt out of your mailing list after an email campaign.
It’s calculated as (Number of unsubscribes / Number of emails delivered) × 100%.
While some list churn is normal, you want this number to be as low as possible. Industry benchmarks show an average unsubscribe rate around 0.1%–0.2% for eCommerce emails. A sudden spike in unsubscribes can signal that your content or frequency is missing the mark with your audience. Monitoring unsubscribe rate helps you gauge overall list satisfaction; if it creeps up, it may be time to adjust your email content, targeting, or send frequency.
To keep unsubscribe rates low, always deliver relevant, valuable content and avoid blasting your entire list with emails that only appeal to a segment of your audience. Also, ensure subscribers have control over their subscription (for example, allow them to manage preferences) so those who aren’t interested can opt down to fewer emails instead of leaving entirely.
Spam Complaint Rate
Spam complaint rate is the percentage of recipients who report your email as spam.
It’s calculated as (Number of spam complaints / Number of emails sent) × 100%.
This metric is crucial for monitoring your sender reputation. Email service providers (like Gmail) heavily factor spam complaints into whether future emails land in the inbox or get diverted to spam folders. Aim to keep your spam complaint rate below 0.1% (one-tenth of one percent). A rate higher than that can quickly jeopardize your deliverability across the board.
High spam complaints usually indicate recipients weren’t expecting your message or found it irrelevant or misleading. To avoid complaints, always send to people who have explicitly opted in, set clear expectations about what content they’ll receive, and make it easy to unsubscribe (it’s better they leave your list than mark you as spam). Keeping content relevant and not over-emailing subscribers will also help minimize the chance of complaints.
List Growth Rate
List growth rate tracks how fast your email list is growing (or shrinking). It accounts for new subscribers added and subtracts those who unsubscribed or bounced.
It’s calculated as (Number of new subscribers – Number of lost subscribers) / Total subscribers × 100%
List growth rate is typically measured over a period like per month. A healthy list growth rate shows you’re continuously expanding your reach to offset natural attrition. A common target is about 2.5% growth per period, though this can vary by organization. If your list growth rate is negative or very low, it means you could be losing subscribers as fast as you gain them, which will eventually hurt your email marketing results.
Improve list growth by making sign-ups easy and appealing—for instance, include clear email sign-up calls to action on your website, offer incentives (like a discount or useful downloadable content) for joining your list, and encourage satisfied customers to share or refer others. Remember, a larger list isn’t automatically better unless those subscribers are engaged, so focus on quality growth (attracting people who genuinely want to hear from you).
Return on Investment (ROI)
Email ROI measures how much revenue you earn from your email campaigns relative to what you spend on them. It’s often expressed as a ratio or percentage.
It’s calculated as (Total revenue from email campaigns / Total cost of email campaigns) × 100% to get an ROI percentage.
For example, if you spent $500 on email marketing in a month and it generated $5,000 in sales, your ROI is ($5,000/$500) × 100% = 1000%. Industry data shows email marketing’s ROI is exceptionally high, averaging around 3600% (meaning about $36 earned per $1 spent). This makes ROI one of the ultimate KPIs that demonstrates the value of email marketing. Tracking ROI helps you justify your email budget and optimize spend. If certain campaigns or list segments yield a higher ROI, you can allocate more resources to those.
To improve ROI, focus on strategies that increase conversion and customer lifetime value from emails (such as better segmentation, personalized content, and upsell/cross-sell campaigns) while keeping costs in check. Ultimately, ROI ties together many of the other KPIs: by improving deliverability, engagement, and conversion metrics, you will see the payoff in your email ROI.
Summary of Key Email KPIs
The table below summarizes the top email marketing KPIs and their typical benchmarks:
| KPI | How to Calculate | Good Benchmark |
|---|---|---|
| Deliverability Rate | (Delivered emails / Sent emails) × 100% | ≥ 98% (Bounce Rate ≤ 2%) |
| Open Rate | (Opens / Delivered emails) × 100% | 20–40% (typical range; note: can be inflated by MPP) |
| Click-Through Rate (CTR) | (Clicks / Delivered emails) × 100% | ~2% average (all industries) |
| Conversion Rate | (Conversions / Delivered emails) × 100% | ~1–5% (varies by campaign type) |
| Unsubscribe Rate | (Unsubscribes / Delivered emails) × 100% | < 0.2% (lower is better) |
| Spam Complaint Rate | (Spam reports / Sent emails) × 100% | < 0.1% (critical to keep low) |
| List Growth Rate | ((New subscribers – Lost subscribers) / Total list size) × 100% | ≥ 2.5% per period |
| Email ROI | (Revenue from emails / Cost of emails) × 100% | ~3600% (i.e., $36 per $1 spent) |