MER deliberately ignores attribution. It takes one revenue figure from your own systems and one spend figure across all channels, and divides them. That's the entire calculation.
Its great strength is that it cannot be double-counted or inflated. There is exactly one revenue number and one spend number, both from sources you control. It's unaffected by attribution windows, iOS privacy changes, cookie deprecation, or platforms competing to claim credit.
Its weakness is symmetrical: it cannot tell you which channel to cut. That's a job for incrementality testing and geo holdouts, not for any attribution dashboard.
Formula
MER = Total Revenue ÷ Total Advertising Spend
Use revenue from your commerce or billing system, and spend from platform invoices. Never mix platform-reported revenue into this calculation — that reintroduces the problem MER exists to avoid.
Why MER matters
MER is the only paid-media metric that hasn't degraded as tracking has. As platform-reported numbers have become increasingly modelled, MER's stability makes it the right daily health metric — the number you watch to know whether the machine is working overall.
Reading a MER change
MER falls from 4.2 to 3.4 over six weeks with spend flat. That means revenue fell while spend didn't — worth investigating regardless of what any platform reports. Conversely, if MER holds steady while you scale spend 40%, you're finding incremental demand rather than just re-buying existing customers, which is exactly what healthy scaling looks like.
Benchmarks
- Early-stage DTC, paid-heavy
- 2.0–3.5x
- Established DTC with strong retention
- 4.0–7.0x
Ranges drawn from Digital Squad client accounts and published industry data. Treat them as orientation, not targets — your category may differ substantially.
Common mistakes
Using it to judge individual channels
MER is deliberately channel-blind. Trying to allocate it back to channels reintroduces the attribution problem it exists to sidestep.
Comparing MER across companies
MER depends heavily on brand strength, organic mix, and category. A 6x MER at a brand with strong organic demand and a 2.5x at a pure-paid startup can represent identical marketing quality.
Ignoring organic contribution
MER includes revenue from organic, email, and direct in the numerator. Growing organic makes MER rise without any paid improvement — useful to know, misleading if you attribute it to the ads team.
Where we work on this