How Much Should You Spend on Google Ads for Your E-Commerce Store?

How much should I spend on Google Ads for e-commerce?

UK e-commerce stores typically need a minimum of £1,000-£1,500 per month in ad spend to give Smart Bidding enough data to optimise. The practical floor is 30-50 conversions per month per campaign; your target CPA sets the daily budget. Below that threshold, the algorithm guesses rather than learns, and you pay for the guessing.

The most common budgeting mistake in the accounts we encounter is picking a number that feels affordable rather than one that is mechanically sufficient. A store spending £500 per month on Google Ads is not doing half the marketing of one spending £1,500; it is often doing none, because the budget sits below the data floor that makes Smart Bidding function. This post covers the correct calculation, how to split budget between Shopping and Search, when to increase spend, and how to recognise when the budget is the problem.

What Is the Minimum Google Ads Budget for an E-Commerce Store?

Google's Smart Bidding strategies (target ROAS, target CPA and Maximise Conversion Value) require a minimum of 30-50 conversions per 30-day window per campaign to function reliably. Google's Smart Bidding documentation is explicit on this: below that threshold, the algorithm lacks sufficient signal to make accurate predictions, and performance becomes inconsistent.

The calculation is straightforward. Take your target CPA and multiply it by 30 to find the monthly ad spend floor for a single campaign:

• Target CPA of £30: minimum monthly spend £900, ideally £1,200-£1,500 to leave headroom for the algorithm.
• Target CPA of £50: minimum monthly spend £1,500, ideally £2,000 or more.
• Target CPA of £80: minimum monthly spend £2,400, ideally £3,000 or more.

These are floors, not targets. Running at the exact minimum means Smart Bidding has barely enough data to operate. In the accounts we manage, campaigns comfortably above the conversion volume threshold consistently outperform equivalent accounts running near the floor, regardless of how well everything else is configured. If you are not sure what a realistic CPA target looks like for your category, our post on Google Ads bidding strategy for e-commerce sets out how to arrive at one from first principles.

How Your Target CPA Sets the Right Daily Budget

The correct way to build a Google Ads budget is to work backwards from unit economics, not forward from what feels comfortable to spend.

Start with your average order value (AOV) and gross margin. If your AOV is £90 and your margin is 45%, you have roughly £40 in gross profit per order. After other costs, your maximum tolerable CPA might sit at £25-£35. From there, your daily budget should be at minimum 2x that CPA figure. A £30 target CPA means at least £60 per day (around £1,800 per month). Below that, Smart Bidding gets conservative: it avoids auctions it is uncertain about rather than testing and learning, and you see suppressed impression share rather than genuine underperformance.

Target ROAS is the inverse of the CPA-to-AOV ratio. AOV of £90 with a maximum CPA of £30 gives a ROAS floor of 3x. Set your target ROAS above that floor (typically 3.5-4.5x for Shopping in a healthy account) and let the algorithm find profitable auctions within it. Setting targets too high relative to what the account can actually achieve is one of the most common causes of throttled delivery. Our bidding strategy guide covers how to avoid that mistake in detail.

How to Split Budget Between Google Shopping and Search

For most UK e-commerce stores, Google Shopping should take the majority of Google spend, typically 60-80% of total Google Ads budget. Shopping captures buyers searching for a specific product rather than a solution, meaning they are closer to purchase and usually convert at a lower CPA than equivalent Search traffic.

Search earns budget for branded queries, high-value product-specific terms and competitor capture. It rarely deserves to lead the account unless your product category has limited Shopping inventory, very high average order values, or you are selling in a considered-purchase category where buyers research for weeks before converting.

If you are running Performance Max, the Shopping-vs-Search question becomes less relevant because PMax consolidates formats under one campaign. The more important question is whether that campaign has the conversion volume to learn. Our post on Performance Max vs Standard Shopping covers the structural decision, including when Standard Shopping gives you more control over where your budget actually goes.

When Should You Increase Your Google Ads Budget?

Two signals indicate a budget increase is warranted. The first is Impression Share Lost to Budget, visible in the campaign view. If that figure consistently sits above 20-30%, your budget is actively capping growth: Google has identified profitable auctions it should enter but cannot because the daily cap is reached too early. You are not failing to convert; you are failing to show up.

The second signal is consistent above-target ROAS over a sustained window. If your campaigns have delivered at or above target for 14-21 consecutive days and there is meaningful impression share headroom available, you have evidence the account can profitably absorb more spend.

When you do increase, do it in increments of 15-20% at a time. Larger jumps push Smart Bidding into a new learning phase and often cause a temporary ROAS dip as the algorithm recalibrates its predictions for a larger auction pool. A 15-20% increase held for 14 days before any further change is the cadence we use when scaling accounts, and it keeps ROAS stable through the transition. The full mechanics are covered in our post on how to scale Google Ads without losing ROAS.

What to Do If Your Budget Is Below the Minimum

If your current ad spend sits below the conversion volume floor, the answer is not to abandon Google Ads but to concentrate budget rather than spread it.

Pick one campaign covering your best-margin, highest-converting product range. Run it on Maximise Clicks or Manual CPC until you accumulate 30 conversions over 30 days. At that point, switch to a Smart Bidding strategy with a conservative target. Only once that first campaign is profitable and stable should you expand to additional campaigns or product ranges.

Spreading £800 per month across Shopping, Search and remarketing campaigns means none of them accumulates the signal they need. Concentration wins at limited budgets every time. Before drawing conclusions about whether the budget is working, also check that conversion tracking is recording purchases accurately. Silent tracking errors (where purchases happen but Google Ads does not see them) are a surprisingly common cause of apparent underperformance, and they corrupt the Smart Bidding signal the whole account depends on. Our guide to Google Ads conversion tracking for e-commerce covers the setup and the errors most likely to cause problems.

How to Know If Your Budget Is Currently Wrong

Beyond Impression Share Lost to Budget, look at how Smart Bidding is behaving. An algorithm running below its data threshold gets risk-averse: it chases the cheapest, safest auctions rather than the most commercially valuable ones. You will see lower-than-expected average CPC, a conversion rate that feels flat, and ROAS that looks acceptable on paper while hiding suppressed volume. The account is not failing; it is being overly cautious because the data is too thin to support more aggressive decisions.

Also consider the context of management costs. Our Google Ads management service is priced at £1,500 per month. If your ad spend is a similar amount, a meaningful share of your total Google investment is going on management rather than on reaching customers. As spend scales, that ratio improves considerably, and the economics of working with an agency become proportionally stronger. See our pricing page for how the numbers work across different spend levels.

If you want an objective view of whether your current budget and account structure are correctly calibrated, a free PPC audit will show you both: a wasted-spend breakdown and a clear picture of where impression share is being left on the table.

Frequently Asked Questions

What is the minimum Google Ads budget for an e-commerce store?

The practical minimum is enough to generate 30-50 conversions per month per campaign, which is what Smart Bidding needs to function reliably. Work backwards from your target CPA: if that is £40, you need at least £1,200 per month in ad spend just to hit the floor. Spending less means the algorithm guesses rather than learns.

What percentage of revenue should I spend on Google Ads?

There is no universal rule, but a common starting point for healthy e-commerce businesses is 10-20% of revenue reinvested in paid acquisition. The right number depends on your margins, average order value and growth ambitions. Your target ROAS is the better anchor: set a floor that keeps orders profitable, then let volume decide the spend.

Should I start with a small Google Ads budget and scale up?

Yes, but not below the data threshold. Starting small is sensible; starting too small means you never generate the conversion volume Smart Bidding needs. Concentrate a modest budget on one campaign and your best product range first, build 30 or more conversions over 30 days, then expand.

How long does it take to know if my Google Ads budget is working?

Allow 60-90 days before drawing firm conclusions. The first 30 days are largely a learning phase; the second 30 days show whether optimisations are holding; by 90 days you have enough data to decide whether the account structure and budget are right or need rethinking.