Is MER the same as blended ROAS?

In practice yes. Blended ROAS is total revenue over total ad spend, which is the ratio MER describes. Some teams invert it and quote spend as a percentage of revenue. Same fact, opposite direction.

The same answer as ROAS: it depends on your contribution margin and your repeat rate. There is no industry number worth quoting, and we are not going to invent one.

Should MER include agency fees and creative costs?

It should if you want it to reflect what marketing actually costs. Many teams track a media-only MER alongside a fully loaded one. Pick a definition, write it down, and stop changing it mid-year.

Why is my MER worse than every channel's ROAS?

Because the channel figures overlap and MER does not. Two platforms each claiming the same $100 order produce $200 of reported revenue against $100 of real revenue.

Can I use MER to decide which campaign to cut?

No. MER has no campaign-level view. Use it to size the budget and channel ROAS to decide where inside that budget the money goes.

ROAS vs MER: which number decides what

Short answer

ROAS is per-channel: the revenue a platform claims divided by the spend on that platform. MER, the marketing efficiency ratio, is blended: total revenue divided by total ad spend across everything. ROAS decides what to scale or cut inside a platform. MER decides whether the business is working, because it has one numerator and one denominator and cannot be double-counted the way channel ROAS can.

The two formulas, and what each one hides

ROAS is attributed revenue divided by ad spend, calculated per platform using that platform's own attribution rules. MER is total revenue divided by total ad spend, calculated from your store and your bank.

The difference is not arithmetic, it is who is counting. ROAS asks a platform how much credit it deserves, and the platform answers generously. MER asks your store what came in and your ad accounts what went out, and neither of those has an opinion about attribution.

ROAS numerator: revenue the platform claims, usually including view-through and modelled conversions.
ROAS denominator: spend on that one platform.
MER numerator: all revenue the business took, including organic, email and repeat purchases you did not pay for.
MER denominator: all paid media spend, across every channel.

Which is how a set of healthy channel ROAS figures can sit on top of a MER saying the business is losing money. Both can be arithmetically correct at the same time.

Why they disagree

Add up your channel-reported revenue and it will exceed what your store actually took. Meta credits an order it touched, Google credits the same order, email credits it too, and each report is internally consistent. The overlap grows with the number of channels you run and the length of your attribution windows. The mechanism is in why do Meta and Google both claim the same sale.

MER contains no overlap because there is nothing to overlap. It also contains everything you did not pay for, which is its own distortion. A 4.0x MER on a business that is 70% repeat customers is not telling you your ads are excellent.

Which number for which decision

Scaling or cutting a specific campaign: ROAS. It is the only view granular enough to act on.
Setting next month's total budget: MER. Channel ROAS cannot answer a question about the whole business.
Reporting to a board or an investor: MER, with the repeat-customer share stated so nobody mistakes loyalty for acquisition.
Diagnosing a month that went bad: both. ROAS tells you which channel moved, MER tells you whether it mattered.
Comparing two channels honestly: neither. That needs incrementality testing, because both channels will claim the same customers.

The two ways teams get this wrong

Managing only to channel ROAS is the common one. Every campaign hits target, everyone is pleased, and the bank account disagrees. That happens because each channel measures its own contribution and nobody measures the sum.

Managing only to MER is rarer and more frustrating. MER moves for reasons that have nothing to do with media: a viral post, a large email send, a seasonal spike, a wholesale order landing in the same revenue line. It tells you something is wrong and refuses to say what. It is a thermometer, not a diagnosis.

The position that holds up is MER as the number you steer by and channel ROAS as the number you act on, with a documented gap between them that you understand well enough to explain out loud.

Getting both out of one place

Most teams do not track MER properly because it needs four exports lined up by date, and by the time that is finished the month is over. So it gets done in January and then not again.

Muze connects Meta Ads, Google Ads, Amazon Ads and Shopify through one connection, so total spend against real store revenue is one question rather than a spreadsheet ritual. Shopify stays read-only commerce data. If you would rather do it by hand once to understand it properly, the arithmetic is in how to calculate blended ROAS.

Keep reading

ROAS, definedThe per-channel version and its assumptions.Blended ROAS, definedOne denominator, no double counting.What is a good ROAS?Why the target has to come from your margin.Why do Meta and Google both claim the same sale?The overlap that makes the two numbers diverge.How to calculate blended ROASThe manual version, once, so you trust the automatic one.Blended reportingFour platforms of spend against real store revenue.

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What is the difference between ROAS and MER?