FormulaMER = total revenue / total marketing spend

The marketing efficiency ratio (MER), also called blended ROAS, compares all the revenue your store made with all you spent on marketing. It doesn't care which ad or channel gets credit for a sale.

That is its strength. Each ad platform reports conversions with its own attribution rules, and one sale can be claimed by Meta, Google and an email at once. MER uses your store's real revenue, so double counting can't inflate it and tracking gaps can't shrink it.

Use MER and ROAS together. Platform ROAS helps you choose between ads and ad sets; MER tells you whether the whole marketing budget is working. If you raise spend and MER holds steady, the extra spend is paying off.

  • Set a target MER from your margins, the same way you set a break-even ROAS.
  • Track it weekly, and over longer periods around big sales.
  • Decide what counts as marketing spend (ads, creators, agencies, tools) and keep the definition stable.

Common mistakes: comparing MER between stores with very different shares of returning customers, since repeat buyers bring revenue without new ad spend, and reading it as the result of a single channel.