ROAS is the number agencies love because every platform reports it and every platform flatters it. Any agency worth paying can produce these in a day:
1. Blended MER. Total store revenue divided by total ad spend, all channels. No attribution model to argue about. If this is falling while ROAS is rising, someone is taking credit for your email list.
2. New-customer cost against first-order margin. What it costs to get a stranger to buy, and what you make on that first order. If the first number is bigger than the second, you’re acquiring customers at a loss, and you’d better be very sure about repeat purchase.
3. Share of revenue from new customers. Under 30% and your ads are mostly reminding people who already love you. Over 70% and you may not be keeping anyone.
None of these show up in a default Ads Manager view. That’s the point. They’re your numbers, not the platform’s.
Which of the three could your team produce today?
Blended MER: the revenue-to-spend reality check
Most platforms report ROAS on their own terms—usually last-click, platform-attributed revenue divided by spend. That number almost always looks better than the truth. Blended MER strips that away. It is simply every dollar your business made from all channels divided by every dollar you spent on ads across all channels. No attribution windows, no platform bias.
If your blended MER is falling while ROAS is climbing, the discrepancy tells you something immediately: your ads are capturing people who would have bought anyway—perhaps from an email campaign, an organic search, or repeat purchase. You are not growing; you are merely taking credit for existing demand.
New-customer cost vs. first-order margin: the profitability gate
This is the metric that separates vanity from viability. Many brands can show a positive ROAS while losing money on every new customer. To calculate this, divide the total ad spend attributed to new customers by the number of new orders, then compare that cost to your actual margin on the first purchase.
If the cost to acquire a new customer exceeds the profit you make on their first order, you are acquiring customers at a loss. The only reason to accept that is a very high confidence in repeat purchase economics. Without that confidence, you are simply buying market share at a loss—a strategy that works for few and fails for most.
Share of revenue from new customers: the growth balance
This number answers a simple question: of all the revenue your business generated in the period, how much came from people who had never bought from you before?
If the share is under 30%, your ads are mostly functioning as retention tools—reminding people who already love you to buy again. That is not growth; it is maintenance. If the share is over 70%, you may be acquiring aggressively but failing to retain. The sweet spot for a healthy growth engine sits between those two thresholds, where you are bringing in enough new revenue to offset natural churn.
Why these numbers matter
These three metrics exist because default Ads Manager views are designed to flatter the platform, not inform your business. ROAS, CPC, CTR—they are platform metrics first, business metrics second. The three numbers above are business metrics first. They require pulling data from your ecommerce platform, your CRM, and your ad platforms, then combining them in a way the platforms never will.
Any agency worth paying should be able to produce these in a day. If they cannot, or if they push back with “the attribution model is complicated,” that is a signal worth noting.
Which of the three could your team produce today?