Cross-platform ROAS comparison: Google Ads vs Meta in 2026

Why platform ROAS figures are not directly comparable

Google Ads and Meta use different attribution models, different counting windows, and different conversion definitions by default. A Google ROAS of 4.2 likely uses last-click attribution with a 30-day conversion window. A Meta ROAS of 3.1 likely uses 7-day click and 1-day view attribution, which double-counts conversions that also appear in Google.

The result: both numbers are correct by their own definitions and both overstate their respective contribution to total revenue. The overlap is your attribution fog.

The three comparison frameworks

Same-window last-click — Force both platforms to a 7-day click-only window and compare. This undercounts Meta (which relies heavily on view-through for DTC brands) but at least compares apples to apples.

Incrementality testing — Turn one platform off for a week (geo-holdout or time-holdout) and measure revenue impact. The most accurate but takes time and accepts temporary revenue loss.

MTA (multi-touch attribution) — A third-party model that assigns fractional credit across all touchpoints. Accurate but requires a clean data pipeline across both platforms.

Using SpendSignoff to pull normalized figures

SpendSignoff queries both platforms via their respective reporting APIs and normalizes the metric names into a common schema: spend, conversions, conversion_value, roas_calculated. The roas_calculated field is always conversion_value / spend regardless of platform — stripping out platform-specific blended figures.

Ask your AI client: "Show me 30-day ROAS for all campaigns across Google and Meta, normalized to conversion value divided by cost." The AI calls query_entities for both platforms and returns one combined table. This does not fix attribution overlap, but it at least removes metric-definition differences.

"Compare my Google and Meta campaigns by calculated ROAS for the last 30 days.
Use conversion_value / cost for both. Flag any campaign where the platform's
native ROAS differs from the calculated figure by more than 20%."

What the comparison typically reveals

In most DTC accounts, Google Search has the highest calculated ROAS because it captures demand that already exists — someone searching for your product is already close to buying. Meta ROAS tends to be lower on a last-click basis but drives a larger share of new customer acquisition.

The correct budget allocation question is not "which platform has higher ROAS" but "at what marginal spend does each platform's next dollar of investment return a positive increment?" That requires incrementality testing, but the normalized ROAS comparison tells you where to start the test.

Drafting budget shifts based on the comparison

Once you have a view you trust, you can ask SpendSignoff to draft reallocation changes: "Shift $200/day in budget from Meta campaigns with calculated ROAS below 2.0 to the Google Shopping campaigns with ROAS above 5.0." The AI stages the decreases and increases as separate before→after drafts in your approval queue. You review each one before anything moves.