Google Ads for Ecommerce: Search, Shopping & PMax Explained
Google Ads captures demand that already exists. Here's how Search, Shopping, and PMax work — and how to structure an account that doesn't waste budget.
Jakob Sperber
Director
Google Ads
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Google Ads captures demand that already exists. Someone searches for your product, your ad appears. That's fundamentally different from Meta or TikTok, where you're creating demand from scratch. For ecommerce, this means Google is typically your most efficient acquisition channel on a last-click basis.
This guide covers the three campaign types that matter, how to structure your account, and the measurement mistakes that lead to bad decisions.
The Three Campaign Types
Search Campaigns
Brand Search captures people searching your brand name. ROAS is always high (8–20x+) because these people already know you. Run it separately from non-brand — it's a conversion channel, not an acquisition channel.
Non-Brand Search captures category-level intent. "Buy running shoes Australia," "best organic dog food." This is true acquisition — new customers who didn't know you before. ROAS is lower (3–8x) but the customers are genuinely incremental.
Key point: Always separate brand and non-brand. Blending them makes non-brand look better than it is and brand look less efficient than it is. You can't make good budget decisions with blended data.
Shopping Campaigns
Product-level ads with images, prices, and reviews shown directly in search results. For ecommerce, Shopping typically drives the most volume and the best efficiency after brand search.
Feed quality is everything. Your product titles, descriptions, images, and pricing determine where and when your products appear. A well-optimised feed outperforms a higher budget with a poor feed every time.
Segment by margin. Not all products deserve the same ROAS target. A 70% margin product can afford a 2x ROAS. A 30% margin product needs 4x+. Use custom labels to group products by margin tier and set targets accordingly, based on your unit economics.
Performance Max (PMax)
Google's automated campaign type that runs across every surface: Search, Shopping, Display, YouTube, Discovery, Gmail. You provide assets and Google decides where to show them.
The biggest problem: PMax cannibalises brand search. It claims credit for conversions from people who already knew you, inflating its reported ROAS. Run a separate brand Search campaign and monitor for cannibalisation. Your actual ROAS is almost certainly lower than what PMax reports.
PMax works best for broad catalogues (50+ SKUs) with sufficient conversion data (50+ per month). For smaller stores, standard Shopping gives more control.
Account Structure
A clean account structure prevents budget waste and enables clear measurement:
Brand Search — low budget, high ROAS, separate campaign
Non-Brand Search — acquisition focused, keyword-targeted
Standard Shopping — top SKUs, margin-segmented
PMax — long-tail catalogue, or omit entirely if <50 SKUs
Separate new customer acquisition from returning customer campaigns. The economics are completely different — a returning customer costs $1–3 to convert via email, while a new customer might cost $40–80 through paid search.
Bidding Strategy
tROAS (target ROAS) is the default for most ecommerce accounts. Set your target from your break-even ROAS calculation (1 / CM1%), not an arbitrary number. For the full framework, see our guide on ROAS benchmarks.
Maximise Conversion Value (no target) gives Google permission to spend at any efficiency level. Always set a tROAS floor.
Campaigns need ~50 conversions/month for automated bidding to work. Below that, you're in perpetual learning phase. Consider manual CPC for low-volume campaigns.
Measurement: Platform ROAS Is Inflated
Google Ads reports its own ROAS using its own attribution model. This number is always higher than reality because Google takes credit for conversions that would have happened anyway (especially brand search).
Calculate actual ROAS: pull your Shopify revenue for the period, divide by total Google Ads spend. That's your real number. Use new customer CAC for acquisition campaigns specifically — not blended metrics.
At the business level, track MER (total revenue / total marketing spend) as the truth layer that sidesteps attribution problems entirely.
Budget: Set It From Your P&L
Your Google Ads budget should come from your margin structure, not a percentage of revenue or what competitors spend. The formula: CM2% minus fixed cost% minus profit target% = allowable marketing spend as a % of revenue. Allocate to Google based on channel efficiency.
Common Mistakes
Running only PMax. You lose visibility into what's actually working. Always run brand Search separately.
Not separating brand from non-brand. Makes your account look more efficient than it is.
No negative keywords. Search campaigns without negatives waste 20–40% of spend on irrelevant queries.
Using platform ROAS for decisions. Always cross-reference with Shopify revenue.
Same ROAS target across all products. High-margin and low-margin products need different targets.
The Bottom Line
Google Ads is the most efficient demand-capture channel for ecommerce. Structure your account to separate brand from acquisition, segment by margin, and measure against your actual unit economics — not what Google's dashboard tells you. The brands that win on Google aren't spending the most. They're spending the smartest.
