MER vs ROAS Calculator: See What Your Platforms Over-Claim

MER is total store revenue divided by total marketing spend, and it is the number ad platforms cannot inflate. Enter one period's store revenue and spend, then add what up to three platforms report. The calculator puts MER, blended ROAS and each platform's own ROAS side by side, and shows how much revenue the platforms claim between them.

Store and spend, same period

Total store revenueFrom your store backend, not an ad platform.

Paid media spendEvery ad platform combined.

Other marketing costsAgency retainers, software, creator fees. Leave blank if none.

Platform 1 (optional)

Platform name

Spend on this platform

Revenue the platform attributes to itself

Platform 2 (optional)

Platform name

Spend on this platform

Revenue the platform attributes to itself

Platform 3 (optional)

Platform name

Spend on this platform

Revenue the platform attributes to itself

CalculateClear

Enter your store revenue and spend for the same period, then press Calculate.

Your MER and ROAS

MER (fully loaded)	-
Blended ROAS (paid media only)	-
Total marketing spend	-
Platform-claimed revenue as a share of store revenue	-

When the platforms claim more revenue than your store booked, the real question is which ads actually move orders.

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What the calculator tells you

Three views of the same period, from the most honest to the most flattering.

• MER divides store revenue by everything you spent on marketing: media plus retainers, software and creator fees.
• Blended ROAS divides store revenue by paid media alone.
• Platform ROAS is what each ad platform reports: the revenue it credits to itself over what you spent on it.
• Platform-claimed share adds up every platform's attributed revenue and sets it against what the store actually booked.

How to read your result

A platform-claimed share above 100% means the platforms are counting the same orders more than once. Each one credits itself for any sale its ad touched, so a buyer who saw a Meta ad and then clicked a Google ad gets counted twice. Even under 100%, the platforms may be claiming orders that email, organic search or direct traffic would have brought in anyway.

Judge the business on MER and judge channels on platform ROAS, then watch both together. Platform ROAS climbing while MER slides usually means the platforms are claiming sales that would have happened anyway. If the gap between summed platform revenue and store revenue passes 15%, fix attribution before you make scaling decisions on platform numbers.

The formula in plain words

1. Total marketing spend = paid media + other marketing costs.
2. MER = total store revenue / total marketing spend.
3. Blended ROAS = total store revenue / paid media spend.
4. Platform ROAS = revenue the platform attributes to itself / spend on that platform.
5. Platform-claimed share = sum of platform-attributed revenue / total store revenue.

Use the same date range for every input, and take revenue from your store backend, not from an ad dashboard. Setting MER targets from your gross margin, and what to do when MER and ROAS disagree, is in our guide to MER vs ROAS.

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