Most Google Ads campaigns optimise for conversions. The problem is that not all conversions are worth the same amount. A customer who buys a ฿300 item and one who buys an ฿8,000 item both show up as "1 conversion" in your dashboard — unless you tell Google they're different. If you don't, the algorithm gravitates toward the cheapest conversions it can find. That's usually your smallest orders.
Value-Based Bidding fixes this by passing the actual transaction value back with every conversion. Google learns which users and queries lead to high-value purchases, then bids more aggressively for those users going forward.
What Value-Based Bidding actually does
Standard Smart Bidding strategies like Target CPA work like this: you set a maximum cost per conversion, and the algorithm finds as many conversions as it can within that budget. Clean and simple, but it treats all conversions as equal.
A ฿300 purchase and a ฿5,000 purchase both count as one. The algorithm has no way to know which one you'd rather have more of.
Value-Based Bidding adds a signal. You send the conversion's monetary value back to Google every time someone converts:
- Customer buys ฿1,500 worth of product → you pass value: 1500
- Customer buys ฿4,200 worth of product → you pass value: 4200
Google builds a model around which user types, search queries, and behaviours tend to lead to high-value purchases, then bids more for those users in the auction.
When to use it
Your product has multiple price points
If you sell a ฿2,500 starter package and a ฿9,000 premium package in the same campaign, Target CPA will keep steering toward the starter package. It's the cheaper conversion.
Google doesn't know the ฿9,000 package is better for your business unless you send a conversion value of 9000 when someone buys it. Without that signal, the algorithm is optimising for the wrong thing.
Your eCommerce order values vary widely
If Average Order Value ranges from ฿300 to ฿5,000 depending on what a customer selects, you're almost certainly leaving revenue on the table with Target CPA. The algorithm finds the cheapest conversions, which tend to be your smallest orders.
When to skip it
How to set it up
Step 1: switch conversion action to dynamic values
Google Ads → Goals → Conversions → select your conversion action → under "Value", switch from "Use the same value for each conversion" to "Use different values for each conversion"
Step 2: pass the real order value through your tag
Using gtag.js directly:
gtag('event', 'purchase', {
'value': ORDER_TOTAL, // the real order amount, every time
'currency': 'THB'
});
Using Google Tag Manager: pull Order Total from the Data Layer, map it to a GTM variable, then reference that variable inside your Conversion tag.
Step 3: switch your bidding strategy
Campaign Settings → Bidding → switch from Target CPA to Maximize Conversion Value or Target ROAS. Add a Target ROAS value if you have a clear revenue target.
The failure mode nobody warns you about
Sending incomplete conversion values
This is the most common reason Value-Based Bidding underperforms. Your tag fires the conversion value correctly for some purchase paths but not all. Maybe the thank-you page doesn't load when a customer pays via a third-party gateway. Maybe a redirect skips the tag entirely.
Google ends up with mixed signals: some conversions have values, some show ฿0. The algorithm can't build a reliable model and starts behaving like a worse version of Target CPA.
How to catch it: go to Reports in Google Ads, add the "Conv. value" column, and scan for rows showing ฿0 or blank. More than 10% missing values means your tracking has gaps that need fixing before Value-Based Bidding will work.
Sending the wrong type of value
Some advertisers pass estimated Lifetime Value or gross profit margin instead of the actual transaction amount. That's valid, but only if you apply the same logic consistently to every single conversion. Mix the two approaches and your ROAS numbers in Google Ads stop matching your actual accounting. You won't notice for weeks — by which point you've been optimising hard in the wrong direction.
Quick reference
| Situation | Strategy |
|---|---|
| Single-price product, all conversions equal value | Target CPA |
| Multiple price points, no clear ROAS target yet | Maximize Conversion Value |
| Multiple price points, clear ROAS target | Target ROAS |
| Fewer than 30 conversions/month | Target CPA first, migrate later |
What to do next
Start by pulling up the "Conv. value" column in your Google Ads Conversion report. If every row shows the same number, you're sending a flat value and Google doesn't know which orders were bigger. If you see rows showing ฿0, your tracking isn't firing consistently across all purchase paths.
Once the tracking is clean, run a blueprint in AdBlueprint. If your campaign has meaningful variation in order values, the Bidding Strategy section will flag it and walk you through the specific migration steps based on your account's actual ROAS history.