MER calculator
This calculator divides all the revenue your store made in a period by all the marketing money you spent in that same period. The result is your marketing efficiency ratio, a whole-business number that ignores which platform claims credit for which sale. It also shows the reverse view, marketing spend as a share of revenue, which is often easier to discuss with a finance person. It does not split results by channel, it does not know your margin, and it cannot tell you which campaign to cut. It answers one question: taken together, how much revenue did each marketing dollar sit alongside?
MER
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- Marketing spend as a share of revenue
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Plain arithmetic on your inputs. Nothing is sent anywhere. Not a forecast.
What the calculator does with your two numbers
MER is total revenue divided by total marketing spend. Say a store took 100,000 dollars in a month across every channel, including organic search, email, direct visits and every ad platform, and spent 20,000 dollars on ads, agencies, tools and creative. The MER is 5.0x. The second output flips that: 20,000 divided by 100,000 is 20 percent, so marketing consumed a fifth of revenue. The two outputs carry the same information. Use whichever one your team finds easier to hold in their head.
How to read MER next to ROAS
Platform ROAS tells you what a campaign claims. MER tells you what the bank account saw. When ROAS climbs and MER stays flat, the platform is probably taking credit for orders that would have happened anyway. When MER falls while every campaign reports a good ROAS, spend is cannibalising organic or email revenue. Track MER monthly on the same calendar as your accounts. It moves slowly, which is the point: it is the number that shows whether growing the ad budget grew the business.
Why MER moves when you fix the other levers
Because the numerator is all revenue, MER improves whenever any lever improves, not only when ads get cheaper. A better conversion rate lifts revenue from the same traffic. A higher average order value lifts revenue from the same orders. A stronger repeat purchase rate adds revenue from customers you paid for months ago. If MER has been sliding, the reason is as likely to be a slower site or a weaker offer as a worse campaign. Check the four levers before you reach for the budget.
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Want these numbers read for you?
Send your store. The plan runs your real figures through the four levers.