If you had to pick one number to check whether your email marketing is actually working, what would it be?

Most course creators would say open rate, or click-through rate, or total list size. All reasonable guesses, but all missing the number that actually answers the question.

The number that matters is revenue per subscriber: total revenue from a promotion, divided by how many people were on your list when you sent it.

Not opens, not clicks, not how big your list has gotten, but what each person on that list is actually worth to your business.

Here's why that distinction matters, and a real example of what happens when you finally start tracking it.

• Open rate tells you whether your subject line worked.
• Click rate tells you whether your email got someone to take one more step.
• Total list size tells you how many people have, at some point, handed over their email address.

None of those numbers tell you whether your email marketing is actually making money — and worse, all three can look perfectly healthy while revenue stalls or declines.

The clearest sign something's missing: a list that grows and grows, while launch results stay flat or even shrink. That's confusing if you're only watching list size. It stops being confusing the moment you start watching revenue per subscriber instead.

What this looks like in real life

One of my coaching clients was looking at a recent campaign and feeling like something had gone badly wrong.

"16,000 is not a small list in any stretch," he told me, "and only 24 people bought." A big list, a real offer, and a buyer count that felt small next to it. The instinct in that moment is almost universal — something must be broken, in the list, the offer, or both.

But total list size was never the number that should have driven that panic. We pulled up two specific launches of the same product, roughly two years apart, and compared them properly.

The first time he'd launched it, back when his list was considerably smaller, the launch brought in $42,000 — $35,000 after affiliate payouts — which worked out to roughly $1.37 in revenue for every subscriber on the list at the time.

Two years later, the list had grown substantially. More subscribers, more reach, more names in the database by any surface-level measure and yet the equivalent launch didn't scale up to match — it landed in a similar total revenue range to the much smaller list from years before.

Looked at through total list size alone, that seems like a real problem: the list nearly doubled, and revenue didn't, but that's exactly the wrong lens.

The real story is that revenue per subscriber dropped, meaning the newer, larger list wasn't converting at the same rate per person as the smaller, more engaged one had.

A bigger list earning the same total revenue as a smaller list isn't standing still — it's losing value per person, and total revenue alone will never show you that.

Why this is the number to build your evaluation around

Total list size only ever goes up. It's a running count, not a health metric, while revenue per subscriber is the number that tells you whether the list is actually getting healthier as it grows, or just getting bigger.

Aggressive growth tactics — broad lead magnets, giveaways, loosely targeted traffic — can inflate subscriber count fast while dragging revenue per subscriber down, because a lot of those new names were never a strong fit to begin with. A smaller, more intentionally built list can meaningfully out-earn a much larger one, person for person, and you'd never catch that difference by watching open rates or list size alone.

How to actually use it

Take your last two or three promotions of the same offer. For each one, divide total revenue by the size of your list at the time you sent it. If that number is holding steady or climbing as your list grows, your growth and your revenue are moving together — genuinely good news. If it's dropping, that's not proof your offer stopped working or your emails got worse. It's a sign the list is growing faster than it's converting, and it's worth understanding why before assuming anything is broken.