You check Meta Ads Manager: ROAS of 4.2×. Then Google Ads: ROAS of 3.1×. TikTok Ads: ROAS of 2.8×. So Meta is your best channel, right? Not necessarily.
Each platform calculates ROAS differently — and if you're making budget decisions based on those numbers alone, you're almost certainly misallocating spend.
Why platform ROAS numbers lie
Each ad platform has a fundamental incentive: make itself look as good as possible. Meta Ads uses a 7-day click + 1-day view window. Google Ads uses a 30-day click window. The result: when you add up all platform ROAS numbers, total attributed revenue is often 2-3× your actual Shopify revenue. Every platform claims credit for the same customers.
The right way: Blended ROAS
Blended ROAS (also called MER — Marketing Efficiency Ratio) is the simplest and most honest metric:
Blended ROAS = Total Revenue ÷ Total Ad SpendExample: Shopify revenue last 30 days: £42,000. Total ad spend (Meta + Google + TikTok): £14,000. Blended ROAS: 3.0×. This number doesn't lie. It doesn't care which platform claims what.
ROAS benchmarks by industry (2026)
| Industry | Average | Strong |
|---|---|---|
| Fashion & Apparel | 3.2× | 5.0×+ |
| Beauty & Skincare | 3.8× | 6.0×+ |
| Home & Garden | 2.9× | 4.5×+ |
| Health & Supplements | 3.5× | 5.5×+ |
| Electronics | 2.4× | 3.8×+ |
| Pet Products | 3.4× | 5.2×+ |
The break-even ROAS formula
Break-even ROAS = 1 ÷ Gross Margin %If your gross margin is 60%, your break-even ROAS is 1 ÷ 0.60 = 1.67×. Any blended ROAS above that means you're profitable on advertising.
Key takeaways
Platform ROAS numbers are not directly comparable. Blended ROAS is your most honest metric. Calculate your break-even ROAS before setting targets. Use platform ROAS for relative trend tracking only, not as absolute benchmarks.