Blended ROAS vs Platform ROAS: Why Ad Platforms Overcount
Short answer: Platform ROAS is the return each ad platform reports using its own attribution, so several platforms can claim the same sale. Blended ROAS divides your real total revenue by your total ad spend across all platforms, so nothing is counted twice. Use platform ROAS to compare campaigns inside one platform, and blended ROAS to judge the business.
Why the platforms' numbers don't add up
Imagine Shopify shows $412k in sales for the month. Meta reports that its ads drove $390k, and Google reports $160k. Together that's $550k, more than you actually sold. Each platform credits a sale to its own ads if a customer clicked or viewed one within its attribution window, so one order can be claimed by several platforms.
How to calculate blended ROAS
Blended ROAS = total revenue ÷ total ad spend. If you made $412k and spent $100k across Meta, Google and TikTok, blended ROAS is 4.1x. Some teams call this MER, the marketing efficiency ratio.
Add cost per new customer
Blended ROAS can look healthy while you mostly sell to existing customers. Cost per new customer = total ad spend ÷ new customers acquired. Tracking both shows whether your ads are actually growing the business.
When platform ROAS is still useful
Inside one platform, its own ROAS is fine for comparing campaigns, ad sets and creatives with each other. The mistake is adding platform ROAS across channels, or using it to judge total profit.
Questions to ask your data
- “What is our blended ROAS and cost per new customer this month, and how did it change?”
- “Which channel returned the most profit per ad dollar last month?”
- “Show each platform's claimed sales next to real Shopify orders.”
Frequently asked questions
Is blended ROAS the same as MER?
Yes, they're the same idea: total revenue divided by total marketing or ad spend across every channel.
Should I stop looking at Meta's ROAS?
No. Use it to compare campaigns within Meta. Just don't add it to other platforms' numbers or treat it as your real return.
Does blended ROAS replace attribution tools?
It doesn't replace pixel or survey-based attribution, but it's the simplest check that can't double count, so it's the best number for judging overall ad efficiency.
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