If you run both Meta Ads and Google Ads for your Shopify store, you have probably compared the purchase conversions each platform reports for the same period and found they do not agree — and that when you add them together, they exceed your actual Shopify sales. This is one of the most common sources of confusion in ecommerce advertising, and understanding why it happens is essential for making sound budget decisions.
Why Meta and Google Attribution Differ
Different default attribution windows
Meta’s default: 7-day click, 1-day view.
Google Ads default: varies by account (often 30-day click with data-driven or last-click model).
GA4 default: last-click, session-based.
A customer who clicked a Meta ad on Monday and a Google ad on Wednesday and purchased on Friday will be claimed by both. Within Meta’s 7-day click window: yes. Within Google’s 30-day click window: yes. Meta and Google each count it as their conversion.
Different counting methods
Meta counts conversions as attributed to the most recent ad in its window. Google counts the conversion and distributes credit according to its attribution model (last-click or DDA). Neither model accounts for what the other platform did.
Both platforms can only see their own touchpoints
Meta cannot see Google Ads clicks. Google cannot see Meta ad impressions. Each platform is running its own attribution calculation in a silo, based on incomplete information about the full customer journey.
Which Platform Should You Trust?
Neither should be trusted in isolation for cross-channel budget decisions. But here is how to assess each:
When Meta data is more reliable
- For measuring Meta creative and audience performance against each other (A/B tests within Meta)
- For optimising Meta campaigns (the platform optimises to its own conversion signal)
- For understanding which Meta campaign types work best for your store
When Google data is more reliable
- For measuring Google Ads keyword and campaign performance
- For branded search conversions (users actively searching your brand name are high intent, and Google captures the moment of decision)
- For GA4 last-click attribution as a cross-platform comparator
When neither platform data is reliable
- For determining which channel deserves more budget when both are running simultaneously
- For calculating total return on ad spend across your full account
- For making incremental budget decisions based on platform-reported ROAS
The Right Approach: GA4 as the Common Language
GA4 with UTM parameters provides a consistent, platform-agnostic view of last-click attribution across all channels. To compare Meta and Google fairly in GA4:
- Confirm UTMs are on all Meta Ads campaign URLs (utm_source=facebook, utm_medium=cpc)
- Confirm Google Ads auto-tagging is on, or add UTMs to all Google campaign URLs
- In GA4, go to Reports → Acquisition → Traffic Acquisition, filtered to the comparison period
- Compare Revenue, Conversions, and ROAS for google / cpc vs facebook / cpc
GA4 last-click revenue tells you which platform was the last touchpoint before purchase. This undervalues awareness channels and overvalues conversion channels, but it is consistent and comparable across both platforms.
The Three-Number Reconciliation
For a cleaner picture, track these three numbers each month:
- Meta Ads Manager reported conversions
- Google Ads Manager reported conversions
- Shopify actual orders
The ratio of (Meta + Google reported) to Shopify actual is your attribution overlap ratio. If the sum is 2x your actual orders, your platforms are collectively claiming 2x what you sold. This does not mean either platform is wrong — it means overlap is high, which typically happens when customers regularly interact with both platforms before purchasing.
What High Attribution Overlap Tells You
High overlap (Meta + Google reported > 1.5x actual orders) suggests your customers routinely see ads from both platforms in their journey. This is a signal that reducing spend on either platform may have less impact than the platform-reported ROAS would suggest, because the other platform also touches most customers.
Low overlap (Meta + Google reported ≈ actual orders) suggests minimal cross-platform customer journeys. Each platform is largely reaching different customers or different journey stages.
Get a Clear Picture of Your Attribution
The first step to understanding Meta vs Google attribution is making sure both platforms have accurate conversion tracking in place. If either platform is undercounting due to pixel issues, the comparison becomes meaningless.
Book your free Shopify tracking audit here and we will verify both your Meta and Google tracking setups, then help you build a consistent cross-platform measurement framework.