Blended ROAS and MER explained for ecommerce

Every ad platform reports a flattering ROAS. Meta says 4.2x, Google says 5.1x, TikTok says 3.8x. Add up the "attributed" revenue and it's somehow bigger than your actual sales. That's the problem with per-platform ROAS — every channel claims the same orders, and post-iOS tracking gaps make it worse. The fix is to stop trusting the platforms' math and measure at the top.

What is MER?

MER — marketing efficiency ratio — is the simplest possible number:

MER = Total revenue ÷ Total ad spend

All revenue (every channel, including organic and returning customers) divided by all ad spend across every platform. If you did €100,000 in sales and spent €20,000 on ads, your MER is 5.0. No attribution, no pixel, no double-counting. It can't be gamed because it uses numbers you can verify in your bank account.

Blended ROAS is the same idea expressed as a return: total revenue attributable to paid effort over spend. In practice most teams use MER and blended ROAS interchangeably as the "did marketing pay off overall" number.

Why blended beats attribution for profit decisions

• No double-counting. When Meta and Google both claim a sale, blended math counts it once — because it starts from your real total revenue.
• Privacy-proof. MER doesn't depend on pixels or cookies, so iOS and consent changes don't distort it.
• Decision-ready. It maps straight onto profit: subtract ad spend from contribution margin and you have profit after ads.

From MER to profit after ads

MER alone doesn't tell you if you're profitable — a 5.0 MER can lose money if your margins are thin. Combine it with contribution margin:

Profit after ads = Contribution margin − Ad spend

This is the number that should drive your budget. If raising spend grows revenue but shrinks profit after ads, your MER has dropped below your break-even — even if Meta still reports a 4x.

Your break-even MER

There's a MER below which you lose money. It depends on your margins:

Break-even MER = 1 ÷ Contribution margin %

At a 50% contribution margin, break-even MER is 2.0 — below that, every extra euro of spend costs you. At 33%, it's 3.0. Knowing this one number turns "should I spend more?" from a guess into arithmetic.

Track it across Meta, Google and TikTok in one place

The catch is pulling spend from every platform and revenue from Shopify into the same view, every day. Margeny connects Meta, Google Ads and TikTok alongside your store and shows MER, blended ROAS and profit after ads in one blended P&L — so you optimize against the number that's actually yours.