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How to Calculate Blended ROAS (and Why It Beats Channel ROAS)
Every ad platform tells you its own ROAS — and they all take credit for the same sales. Add them up and the numbers lie. Blended ROAS (the same figure as MER) fixes that by measuring your whole marketing engine at once: total revenue over total ad spend.
Here's how to calculate it and why it's the number a founder should watch.
Blended ROAS & MER Calculator
Your numbers
Total revenue and every channel’s ad spend — results update instantly.
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All channels, this period
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Revenue ÷ spend goal
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MER · blended ROAS
+0.14× vs target4.14×
Total ad spend
$29,000.00
Spend % of revenue
24.2%
Marketing cost ratioThe blended ROAS / MER formula
Blended ROAS = total revenue ÷ total ad spend, where total ad spend is every channel added together (Meta, Google, Amazon, TikTok and any other). A blended ROAS of 4× means every $1 of ad spend is associated with $4 of revenue across the business.
MER (marketing efficiency ratio) is the same calculation — the terms are interchangeable.
Why it's lower than each platform's ROAS
Platforms use overlapping view-through and last-click attribution, so each claims conversions the others also claim. Sum the platform ROAS numbers and you're double-counting. Blended ROAS counts every sale exactly once, so it's always lower — and it's the honest figure for deciding whether to spend more or less overall.
What's a good blended ROAS?
It depends on your margin, not a benchmark. Compare it to your break-even ROAS (1 ÷ contribution margin): above it you profit, below it you don't. A 60%-margin brand can thrive at 2.5×; a 25%-margin brand may need 4×+. Track the trend, not one week.
Also watch: spend as a share of revenue
The inverse view — total ad spend ÷ total revenue — is your marketing cost ratio. Rising spend-as-a-percentage-of-revenue with flat sales is an early warning that efficiency is slipping, often before it shows up in profit.
Frequently asked questions
Is blended ROAS the same as MER?
Yes. Both divide total revenue by total ad spend across all channels. “MER” (marketing efficiency ratio) is the common e-commerce term; “blended ROAS” means the same thing.
Why is my blended ROAS lower than each platform's ROAS?
Because platforms double-count overlapping conversions. Blended ROAS counts each sale once, so it's lower — and more useful.
What's a good blended ROAS?
It's margin-dependent. Compare it to your break-even ROAS rather than a fixed number.
Track this on a live dashboard
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Keep reading
What Is a Good ROAS? Break-even ROAS Explained
A “good” ROAS isn't a fixed number — it depends on your margin. Learn the ROAS formula, how to find your break-even ROAS, and how ROAS relates to ACoS, with a calculator to find yours.
How to Calculate Break-even CPA
Break-even CPA is the most you can pay to win an order before it stops making money. Learn the formula, a worked example, and how to hold your Meta and Google CPA against it.
The Complete Guide to E-commerce Profitability
Revenue is vanity; profit is sanity. Walk the profit ladder — gross, contribution and net — learn which costs belong where, how discounts, shipping and returns bite, and how to find the numbers that tell you if you're actually making money.