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MER calculator

MER, the marketing efficiency ratio, is your store's total revenue divided by your total ad spend on every channel. No ad platform decides what counts, so attribution can't inflate it. Use it to set how much to spend overall, and ROAS inside each platform to decide where the money goes.

From Shopify, after sales tax, for one period.

Facebook and Instagram.

Search, Shopping, Performance Max and YouTube.

TikTok, influencers, anything else paid.

Purchase value in Ads Manager.

Conversion value in Google Ads.

MER
3.33x
Total ad spend
$7,500
ROAS Meta and Google report
4.21x
Share of store revenue they claim
118%
Connect your store and Tera Ads counts sales once, from your orders, beside what Meta and Google claimFree for one business, no card needed.

The formula

  • Total ad spend = Meta + Google + every other paid channel
  • MER = store revenue ÷ total ad spend
  • Platform ROAS = (sales Meta reports + sales Google reports) ÷ (Meta spend + Google spend)
  • Share claimed = sales the platforms report ÷ store revenue

Worked example

Your store took $25,000 this month.

You spent $5,000 on Meta, $2,000 on Google and $500 elsewhere.

Meta reports $19,000 of sales and Google $10,500.

MER is 3.33x ($25,000 ÷ $7,500). Meta and Google together report a ROAS of 4.21x and claim 118% of what your store took, because both count some of the same orders.

Questions

What is a good MER?

It depends on your margins. Work out the ROAS you need to break even, 1 ÷ your contribution margin before ads, and keep MER above it. A brand that keeps 40% of revenue before ads needs an MER above 2.5 to make money.

Why do Meta and Google claim more than my store took?

Each counts a sale when someone who saw or clicked its ad buys within its attribution window, so one order can be claimed by both. Neither knows when a cash-on-delivery order comes back.

Should MER use revenue after returns?

If you can, yes: use store revenue after cancellations, returns and refunds, so MER reflects money you keep. Whichever you pick, keep it the same every month so the trend means something.

Should I enter order value with or without sales tax or VAT?

Use order value after the tax is taken out, because it isn't yours to keep. Counting it makes every ROAS look better than it is. Keep product cost, fees and ad spend on the same basis.

The full guide

MER vs ROAS: Which Number Should Run Your Ad Budget?ROAS tells you which ads Meta and Google take credit for. MER tells you whether all your ad spend pays. When to use each, and how to set an MER target.

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