ROAS vs MER: which one to trust
ROAS (return on ad spend) is what each ad platform shows you: the revenue it attributes to its own ads, divided by what you spent there. Google Ads, Meta and TikTok each count every sale their ads touched within their attribution window, so when a customer saw a Meta ad, clicked a Google ad and then bought, both platforms claim the same order.
MER (marketing efficiency ratio), also called blended ROAS, ignores attribution. It takes the revenue your store actually made and divides it by everything you spent on ads:
Platform ROAS is useful for comparing campaigns inside one platform. MER tells you whether your marketing as a whole pays off, and it can't be inflated by double counting.
Break-even ROAS
Revenue isn't profit. To know whether an MER is good, compare it with the ROAS at which your ads exactly pay for themselves:
Gross margin here is what is left of a sale after product cost, shipping and payment fees. With a 45% margin, break-even ROAS is 1 ÷ 0.45 ≈ 2.2. Below that, every sale your ads bring costs you money; above it, the difference is what is left for your other costs and profit.
- Margin 70% → break-even ROAS 1.4
- Margin 50% → break-even ROAS 2.0
- Margin 30% → break-even ROAS 3.3
Cost per order
Blended CPA is your total ad spend divided by all orders. Compare it with the most you can pay for an order and still break even:
Why platforms report more than your store made
Add up the revenue each platform reports and you will often get more than your store's real revenue. That gap is double counting, plus view-through conversions and long attribution windows. The calculator above shows it as a percentage: the bigger it is, the less you can rely on any single platform's ROAS to decide where your budget goes.
Selling in several countries or stores? Read how to report across stores, markets and currencies.