Google Ads Bidding Strategies Explained: When to Use Each One for eCommerce

Google's bidding strategies aren't one-size-fits-all—the right choice depends on your campaign maturity, conversion volume, and business goals. We've managed over €20M in Google Ads spend for eCommerce brands, and we've seen firsthand how the wrong bidding strategy can drain 30% of your budget on low-intent clicks, while the right one can unlock 2-3x ROAS growth.

This post breaks down exactly when to use each strategy, how to transition between them, and the data thresholds that make each one viable.

What Are Google Ads Bidding Strategies and Why Do They Matter?

Bidding strategies are the automation rules that tell Google how much to bid for each click. Instead of manually setting bids on every keyword, you set a goal (like "spend no more than €50 per conversion"), and Google's machine learning adjusts bids in real time across thousands of auctions.

For eCommerce brands, this matters because: The right bidding strategy can reduce your cost per acquisition by 15-40% while increasing conversion volume. The wrong one wastes budget on low-intent clicks or leaves money on the table by bidding too conservatively.

Manual CPC: When to Use It (and Why You're Probably Using It Wrong)

Manual CPC (Cost Per Click) means you set the bid for each keyword or ad group manually. Google doesn't optimize—you do.

Use Manual CPC only if your campaign has fewer than 30 conversions per month. Below this threshold, automated strategies lack enough data to learn effectively. Manual CPC is your starting point for new campaigns, seasonal products, or test campaigns with limited budgets.

Real example: A fashion brand launched a new collection with Manual CPC at €1.50/click. After 2 weeks and 8 conversions, they had no reliable data to inform automation. Once they hit 30 conversions (about 6-7 weeks in), they switched to Target CPA—and saw cost per acquisition drop to €32 from €48.

The mistake most brands make: They stay on Manual CPC too long. As soon as you hit 15-20 conversions per month, start preparing to switch. Once you cross 30, automate immediately.

Maximize Conversions: The Training-Wheels Strategy

Maximize Conversions tells Google: "Get me as many conversions as possible within my daily budget, no cost limit per conversion."

Use this when: You're scaling a new campaign and need conversion velocity more than cost efficiency. It's ideal for brands building data for more sophisticated strategies later.

Conversion threshold: Works reliably at 10+ conversions per month.

Here's where Maximize Conversions excels: In the first 30 days of a new campaign, it accelerates learning. Google's algorithm gets constant feedback on which audiences, keywords, and placements convert. This data becomes gold when you graduate to Target CPA or Target ROAS.

The catch: Your cost per conversion will be 20-35% higher than manual or constrained strategies. You're paying for speed and data.

Real scenario: A home & lifestyle brand tested a new traffic source (Pinterest) with Maximize Conversions at €3,000/day budget. In month one, they spent €1,200 on 18 conversions—a €67 cost per acquisition. But by month 2, they switched to Target CPA (€45), and with the learning data from month 1, Google bid more efficiently. They kept the same €3,000 budget but got 35 conversions instead of 15.

Target CPA: The Stability Play for Scaling Campaigns

Target CPA (Cost Per Acquisition) sets a maximum you're willing to pay per conversion. Tell Google "I want to pay no more than €35 per conversion," and it adjusts bids to stay within that target.

Use Target CPA when: Your campaign has 30+ conversions per month and you have a predictable cost ceiling you need to hit.

Conversion threshold: Works best with 30-50+ conversions/month. Below 30, Google won't have enough data to hit your target consistently.

Target CPA is the workhorse strategy for scaling. Brands spending €20K-€50K/month on Google Ads typically use this as their baseline because it balances growth with predictability.

The realism: Google won't always hit your target CPA. During high auction competition, it may bid up to 15-20% above your target to capture good intent. In slow periods, it'll underbid. Your actual CPA will fluctuate ±5-15% around your target—not a hard ceiling.

Example: A beauty brand sets Target CPA at €28 for their best-performing Shopping campaign. Over a month, their average lands at €26 (better than target), but on high-competition days (weekends), they hit €32. Monthly, it averages to the goal. They get predictability, and Google gets room to optimize.

Target ROAS: Maximum Revenue for Mature Campaigns

Target ROAS (Return on Ad Spend) optimizes directly for revenue. Set it to 3.0x, and Google tries to generate €3 in revenue for every €1 spent on ads.

Use Target ROAS when: Your campaign has 50+ conversions per month AND you understand your profit margins.

Why the high threshold? ROAS requires more conversion data to learn effectively than Target CPA. You're not just optimizing for conversions—you're optimizing for profitable conversions. That's a harder problem, so Google needs more examples.

The critical mistake most brands make: They set Target ROAS without understanding their actual margins. If your product costs €40 to make and ship, and you sell it for €100, your margin is €60. A 3.0x ROAS (€3 revenue per €1 ad spend) means €1.33 profit per €1 spent—solid. But if you set 5.0x ROAS without that math, Google can't hit it, and your campaigns will underdeliver.

Real case: A furniture eCommerce brand has a 45% margin on average order value of €420. Their Target ROAS of 2.5x means:

• €1 ad spend → €2.50 revenue → €1.13 profit (assuming 45% margin)
• This is profitable and sustainable.

They tried 4.0x initially, but Google couldn't reliably hit it, so impressions and spend dried up. They dropped to 2.5x, volumes returned, and ROI improved.

Maximize Conversion Value: Premium Revenue Strategy

Maximize Conversion Value tells Google to generate as much total revenue as possible within your budget—no cost ceiling.

Use when: You have 100+ conversions per month, strong conversion data, and you want to maximize absolute revenue (not efficiency).

This is less common for eCommerce than ROAS, but it works for high-volume, mature campaigns where volume matters more than per-unit efficiency.

How to Choose Your Bidding Strategy: The Decision Framework

Here's the framework we use with clients:

| Conversions/Month | Recommended Strategy | Why | |---|---|---| | 0-15 | Manual CPC | Insufficient data for automation | | 15-30 | Manual CPC → Maximize Conversions | Transition phase; build conversion volume | | 30-50 | Target CPA | Balanced growth and cost control | | 50-100 | Target CPA or Target ROAS | ROAS if you understand margins; CPA if you prefer stability | | 100+ | Target ROAS | Enough data for sophisticated optimization |

Practical steps:

1. Audit your current campaign. How many conversions per month does it generate?
2. If you're below 30, stay manual or use Maximize Conversions for 4-6 weeks to build data.
3. At 30+ conversions, switch to Target CPA. Set it at your current average CPA (e.g., if you're averaging €32/conversion, set Target CPA to €30-€32).
4. Monitor for 2 weeks. If conversions drop >20%, raise your Target CPA by €2-5. If it's hitting your target easily, lower it by €2-5.
5. At 50-100 conversions/month, test Target ROAS on a small percentage of the campaign (25%), then scale if it outperforms.

Bidding Strategy Mistakes That Cost Brands 30% of Budget

Mistake 1: Switching strategies too frequently. Google's algorithm needs 2-4 weeks to stabilize after a strategy change. If you flip from Target CPA to Target ROAS every 10 days, you prevent learning. Commit to each strategy for at least 3-4 weeks.

Mistake 2: Setting Target CPA too low. If your actual CPA is €38 and you set Target CPA to €25, Google will underdeliver (limited bid volume). Set your target at or slightly below your current actual CPA, then optimize down over weeks.

Mistake 3: Using Target ROAS without conversion tracking. ROAS is only as good as your conversion value data. If your shopping feed has wrong prices or your conversion value is static (instead of order-value-based), ROAS will misfire. Audit tracking before switching.

Mistake 4: Ignoring seasonality. During high-season months (Black Friday, Christmas), competition and CPCs spike. Your Target CPA may not be achievable. Plan for 15-25% higher CPAs and adjust your strategy or budget accordingly.

Transitioning Between Strategies: The Safe Path

When you're ready to switch bidding strategies, don't flip a switch on your entire campaign. Here's how we do it:

1. Week 1: Test the new strategy on 25% of your campaign budget (via campaign duplication or bid adjustments).
2. Week 2-3: Monitor performance. Compare CPA, conversion rate, and spend between the old and new strategy.
3. Week 4: If the new strategy is performing similarly or better, gradually shift budget (increase new campaign to 50%, reduce old to 50%).
4. Week 5-6: If performance holds, full transition. Keep the old strategy running for 1-2 more weeks as a control before pausing.

This approach reduces the risk of dropping conversions by 50% while you're switching.