Total revenue ÷ total marketing spend. The number that survives iOS 17 attribution loss and tells you if marketing is actually working.
ROAS measures channel-attributed revenue against channel spend. After iOS 17 + 18 broke click-through attribution for ~30% of users, platform ROAS overstates by 20-40% depending on vertical. MER bypasses attribution entirely — it just asks: did all marketing dollars produce more revenue than they cost?
Track MER weekly. A falling MER over 4 weeks signals one of three things: spend grew faster than revenue (over-spending), creative fatigue (no new variants), or customer mix shifted (more cold, less repeat). The fix differs for each. We diagnose this on every free audit.
Pair MER with channel-level ROAS for full visibility. Open ROAS Calculator →