Performance Max is Google's most automated campaign type. It runs across Search, Shopping, Display, YouTube, Gmail, and Discover from a single campaign. For e-commerce businesses, it can be powerful. But "automated" doesn't mean "set and forget." The algorithm is only as good as what you give it, and what you give it is primarily creative assets, audience signals, and product structure.
I took over a PMax campaign for a homeware e-commerce business last year that had been running for four months with a single asset group, three images, no video, and generic copy written to cover every product category. The campaign had spent around £6,000. When I rebuilt it into four category-specific asset groups with proper imagery and tailored copy, cost per purchase dropped by 38% within six weeks. The algorithm hadn't changed. What we fed it had.
The common assumption is that PMax's automation compensates for thin creative. It doesn't. It amplifies whatever you give it, good or bad.
Most underperforming PMax campaigns aren't failing because of the platform. They're failing because the asset groups are thin, the audience signals are vague, or everything is lumped into one group with no ability to analyse what's actually working. For a broader look at the other structural issues that derail Google Ads performance, 20 Ways to Kill Your Google Ads Performance covers the account-level mistakes that compound quietly over time.
What creative assets does Performance Max need?
Performance Max builds ad combinations automatically from the assets you provide. The more relevant assets you supply, the more combinations Google can test, and the more placements it can serve across the network.
For images, Google accepts up to 20 per asset group. You need multiple orientations: landscape (1.91:1 ratio), square (1:1), and portrait (4:5) for different placements. For e-commerce, the images should show products clearly. Use clean product shots on white or neutral backgrounds for Shopping-style placements, and lifestyle images showing products in use for Display and Discovery. Minimum is 3 images to run, but at or near the 20 maximum gives Google far more to work with. Images that differ meaningfully, covering different products, different contexts, and different angles, outperform uploading slight variations of the same shot.
For videos, Google accepts up to 5. If you don't provide any, Google will auto-generate videos from your images and text, and these auto-generated videos are typically poor. Upload your own even if production quality is modest. A simple screen recording with product images and a voiceover is better than the auto-generated alternative. Videos should be at least 10 seconds. Landscape (16:9), square (1:1), and vertical (9:16) formats are all accepted. Vertical video is particularly relevant for YouTube Shorts and Discovery placements.
Headlines and descriptions follow the responsive search ad format: up to 15 headlines (30 characters each) and 5 descriptions (90 characters each). Google assembles these into ad combinations. Each headline should work independently, so don't write them assuming they'll appear together. Cover your main value propositions: product benefits, key differentiators, calls to action, social proof indicators, and location if relevant.
Business name and logo appear on some ad formats. Upload a square logo and a landscape logo. The logo should be clean and legible at small sizes.
Audience signals: giving Google a starting point
Performance Max doesn't use audience targeting in the traditional sense. It will show ads to anyone it believes is likely to convert. But audience signals help it get there faster by showing it who your existing customers and best prospects look like.
The most valuable signal is customer data. Upload a customer list (email addresses or phone numbers, hashed) as an audience signal. Google uses this to find similar users. For e-commerce, a list of recent purchasers is the highest-quality signal you can provide.
Website visitors via Google Analytics 4 audiences, such as purchasers, cart abandoners, and high-engagement visitors, are also worth adding as signals. These are people who've already shown intent.
Under custom segments, you can enter URLs of competitor websites to signal the type of audience you're after. People who visit similar retailers are reasonable prospects.
Adding your most important keyword themes as custom segments (based on searches) helps direct PMax toward search intent, which is particularly important if your campaigns are spending heavily on Display without converting.
Audience signals are signals, not targeting constraints. Google will still show ads beyond these audiences if it predicts conversion likelihood, but the signals accelerate the learning phase significantly. Building remarketing segments separately to use as audience signals is worth doing. Unlocking Hidden Revenue with Google Ads Remarketing Audiences covers how to structure those segments so the highest-intent visitors are properly identified.
Structuring asset groups by product category
One of the most common mistakes with PMax is lumping all products into a single asset group. When everything is together, you have no visibility into which product categories are driving performance and which are burning budget. You also can't write relevant headlines and descriptions, and you end up with generic copy that fits every product and is compelling for none.
Structure asset groups by meaningful product category. An online homeware retailer might have separate asset groups for bedding, kitchenware, lighting, and storage. A clothing retailer would separate by gender, category, or product type. Each asset group should have creative assets relevant to that specific category, headlines and descriptions written for that product type, and a product listing group filtered to those products specifically.
This allows you to see performance by category, add category-specific creative, and eventually pause or adjust budgets at the category level based on what's generating returns.
What to monitor and how often
PMax provides limited transparency compared to standard Google Ads. You can't see individual search terms (though you can request a search terms insight report) and you have less control over which placements receive budget.
Check asset performance ratings regularly. Google rates each asset as "Best," "Good," or "Low." Replace Low-rated assets regularly. Assets rated "Best" give you a signal of what messages resonate. Use that to inform your wider creative direction.
Asset group performance needs a monthly review. Check conversion volume and cost per conversion by asset group. Asset groups spending without converting over a 60-day window warrant review: either the creative is wrong, the audience signals are off, or those products don't work through PMax.
PMax now supports adding search themes, keyword-like inputs that tell the algorithm the types of searches you want to appear for. Add your most important search intent themes to steer spend toward search inventory. For e-commerce businesses in North Wales running PMax for the first time, the asset group structure and audience signals matter far more than the campaign settings. It's worth getting these right before worrying about anything else. If you're running an online store, making sure your Shopify SEO foundations are solid alongside your paid campaigns gives you a stronger baseline to build from.
Google Ads management in North Wales: if you're running Performance Max and want a structured review of your asset groups and campaign setup, get in touch.
