Meta shows 4.2x ROAS. Google shows 3.8x. Add them up and it looks like a great month. Then you check Shopify revenue against total spend and land at 2.1x. One of these numbers reflects your actual business. The others reflect how each platform has decided to count credit. Here's how to calculate the one that's real.
Meta, Google, and TikTok each calculate ROAS from their own attributed conversion value, using their own attribution window and their own rules for view-through credit. When a customer's path touches more than one platform, which is common, multiple platforms can legitimately claim the same sale. Summed platform revenue routinely exceeds real Shopify sales as a direct result. None of the platforms are wrong by their own definition. They're just each answering "what did I contribute," not "what actually happened."
Blended ROAS = Total Shopify Revenue / Total Ad Spend Across All Channels. This is the same calculation most operators call Marketing Efficiency Ratio, or MER; the two terms are interchangeable, with MER framing it as the efficiency of your whole marketing engine and blended ROAS framing it as a return figure. Either way, it uses your actual Shopify revenue as the numerator, not any platform's self-reported conversion value, which is what makes it impossible to double-count.
Pull ad spend directly from each platform's billing summary, not the campaign reporting view, since daily spend caps and account-level adjustments can make the two differ slightly. Sum spend across every platform into one number, in one currency. For revenue, use Shopify's net sales figure for the same period, matching time zones across all your sources so a sale doesn't land in a different day depending on which system you're checking. Consistency in both inputs matters more than precision in either one.
Once you have blended ROAS, you can measure exactly how much platforms are overclaiming with a second calculation: Overlap Ratio = Sum of All Platform-Reported Revenue / Shopify Revenue. An overlap ratio under roughly 1.15 is healthy, suggesting mostly single-channel customer journeys or reasonably tight attribution windows. A ratio above 1.5 signals a serious double-counting problem, and at that point, individual platform ROAS numbers are close to meaningless for channel-level budget decisions, even though blended ROAS at the business level still holds up fine.
As a rough guide, a 10 to 20 percent variance between platform-reported revenue and Shopify's actual numbers is common and largely unavoidable given how attribution windows and view-through modeling work. A 30 to 50 percent variance usually points to a real tracking issue worth investigating, not just normal attribution noise.
For Shopify brands roughly in the 1 to 20 million dollar revenue range, a blended ROAS below 2 is generally a warning sign unless margins are unusually high. The 2.5 to 4 range is where most healthy brands tend to sit. Above 5 often signals there's room to spend more aggressively and still stay profitable. These are rough bands, not hard rules, since the number that actually matters for your business is the one below.
Breakeven blended ROAS = 1 / Contribution Margin. If you keep 25 cents of profit on every revenue dollar after product cost, shipping, and payment fees, your breakeven is around 4.0. Keep 40 percent margin and breakeven drops to about 2.5. Keep 50 percent and it drops to 2.0. Comparing your blended ROAS against a generic industry benchmark is far less useful than comparing it against your own breakeven number, since two stores with the same blended ROAS can be in completely different financial positions depending on their margin.
1. Pull total ad spend from each platform's billing summary, in one currency, for the same date range. 2. Pull total Shopify net revenue for that identical date range. 3. Divide revenue by spend to get your blended ROAS. 4. Sum every platform's self-reported revenue and divide by your Shopify revenue to get your overlap ratio, as a periodic sanity check rather than a weekly habit. 5. Compare your blended ROAS against your own breakeven number, calculated from your actual contribution margin, not a generic benchmark. 6. Use platform-level ROAS only for optimizing within that specific platform, never for deciding whether to scale total spend up or down.
You will never get Meta, Google, and Shopify to agree on ROAS, and trying to reconcile them to one number is the wrong goal. Blended ROAS, built entirely from your own Shopify revenue and total ad spend, is the one number immune to platform overclaiming. Measure it against your own breakeven, calculated from your real margin, and you have a genuinely trustworthy answer to the only question that matters: is the money coming back.
Use blended ROAS: total Shopify revenue divided by total ad spend across every platform, pulled from each platform's billing summary in one currency for the same date range. Because it's built from your own revenue rather than any platform's self-reported conversion value, it can't be inflated by cross-platform double-counting.
For brands roughly in the $1M-$20M revenue range, below 2 is generally a warning sign unless margins are unusually high, 2.5 to 4 is where most healthy brands sit, and above 5 often means there's room to spend more aggressively. The more precise target is your own breakeven ROAS, calculated as 1 divided by your contribution margin.
Overlap ratio is the sum of every platform's self-reported revenue divided by your actual Shopify revenue. Under about 1.15 is healthy. Above 1.5 signals serious double-counting, at which point individual platform ROAS numbers become close to meaningless for channel-level decisions.
A 10 to 20 percent variance is common and largely unavoidable given how attribution windows and view-through credit work. A 30 to 50 percent variance usually indicates a real tracking issue worth investigating rather than normal attribution noise.