MER vs. ROAS: why the total beats attribution
Nicklas Segatz Mortensen · Growth Hacker · Fractional CMO · Meta Ads Nerd · 8 July 2026 · 4 min.
Short answer
ROAS is often the platform's own attributed revenue for a single channel — and it double-counts across channels. MER is your total revenue against your total marketing spend, with no attribution. For budget decisions across channels, MER beats platform ROAS.
Sådan virker det
Hver platform tilskriver sig de samme salg — lagt sammen bliver det 130 % af den faktiske omsætning. MER ignorerer attribution og måler den samlede omsætning mod det samlede forbrug.
01Why platform ROAS lies about the total
Meta, Google and TikTok each claim credit for the same sales using their own generous conversion windows. Add up their reported revenue and you can hit 130% of what actually came in. Platform ROAS is fine at the ad level, but misleading when you want to know whether the whole machine is making money.
MER cuts through it: total revenue divided by total spend. No attribution, no double-counting — just what came in and what it cost.
Sådan virker det
Hver platform tilskriver sig de samme salg — lagt sammen bliver det 130 % af den faktiske omsætning. MER ignorerer attribution og måler den samlede omsætning mod det samlede forbrug.
02Use each for its own question
ROAS answers "how does this channel or campaign look through the platform's lens." MER answers "is the total marketing effort making money." For day-to-day optimization, platform numbers are useful; for budget decisions across channels and for scaling, MER is the reference point.
A healthy practice: scale by MER, optimize by POAS/ROAS within channels, and validate with incrementality. That way you're not chasing a flattering platform number that never shows up in the bank.
Frequently asked questions
When should I use MER instead of ROAS?+
For budget decisions across channels and for scaling. Platform ROAS double-counts, so it suits optimization within a single channel, but MER is the honest measure of whether the whole effort is making money.
Is a MER lower than platform ROAS a problem?+
No, it's expected — MER isn't inflated by attribution. What matters is whether MER holds or rises as you scale. If it falls, you're buying sales you'd have gotten anyway.
Related terms
Glossary
What is MER?
MER (Marketing Efficiency Ratio) is your total revenue divided by your total marketing spend across every channel. It ignores the platforms' own attribution and shows how efficiently the whole marketing machine is working.
Read the entry →Glossary
What is ROAS?
ROAS (Return on Ad Spend) is the revenue generated by ads divided by ad spend. A ROAS of 4 means €4 in revenue for every ad euro — but says nothing about what you actually keep.
Read the entry →Glossary
What is blended ROAS?
Blended ROAS is your total revenue divided by your total ad spend across every channel. Unlike platform ROAS, it isn't built on attribution and therefore can't be double-counted.
Read the entry →Glossary
What is incrementality?
Incrementality is the added effect a marketing effort creates: the sales that happened only because the ad ran. Sales you'd have gotten anyway aren't incremental — whatever the platform credits.
Read the entry →
Nicklas Segatz Mortensen
Growth Hacker · Fractional CMO · Meta Ads Nerd at Oaksmond
Growth hacker and fractional CMO with 10+ years' experience and hundreds of millions in managed ad spend behind him. Background from larger Danish and international scale-ups, and from the agency world.
Meet the team →