CPA vs ROAS: Which Metric Should Drive Bidding

Both numbers come from the same ad spend and the same conversions. CPA (cost per acquisition) is ad spend divided by conversions. ROAS (return on ad spend) is conversion value divided by ad spend.

When every order is the same size, the two are the same target: ROAS = order value ÷ CPA. A $100 product with a $25 CPA target is a 4.0 ROAS target. So the real question is whether your conversions are worth different amounts.

Google draws the line in the same place. Its Target ROAS help page frames Target CPA as the pick when all conversions are treated equally and Target ROAS as the pick when conversions have different values. For the Google settings in detail, see Target CPA vs Target ROAS.

One catch: if you don't send a value with each conversion, Google uses the default value you entered for every conversion (Google Ads Help). Every sale then looks identical, so ROAS bidding has nothing extra to weigh. That conclusion is ours, not Google's.

Starting in June 2026, Google is relabeling "Maximize conversions with a Target CPA" as "Target CPA" and "Maximize conversion value with a Target ROAS" as "Target ROAS" (Google Ads Help). Google's developer blog post of June 16, 2026 calls this decoupling the targets from Maximize conversions and Maximize conversion value. Those two stay available for getting the most volume from a budget without a set target.

For the renaming, Google says the underlying bidding behavior stays exactly the same and you don't need to take any action in your account. It also says the names you see may differ slightly during the transition.

The change that does move results came on 17 August 2026. Google says that before it, campaigns with a "Limited by budget" status on a target-based strategy (for example Target CPA or Target ROAS) could overperform their targets and swing when budgets changed. Now those campaigns perform more consistently toward the target, including when you adjust the budget (Google Ads Help). Google lists Search, Shopping, Performance Max and Demand Gen as covered, and says App, Video reach and Video view campaigns keep the previous behavior.

Google's example: a budget-constrained campaign with a $10 Target CPA that was actually getting conversions at $5 now delivers closer to $10. Google won't adjust your targets or budgets for you, and campaigns that were beating their target may see some volatility.

On Meta the matching settings go by other names. Meta groups bidding into spend-based, goal-based and manual, and the goal-based options are cost per result goal and ROAS goal (Meta Business Help Center).

Cost per result goal sets the average cost you want and gets as many conversions as it can near that cost. To use it, choose Maximize volume of conversions as the performance goal at the ad set level (Meta). Meta says it may spend less than your full budget when the market is competitive, to protect the cost target, while Highest volume puts spending the full budget first.

A ROAS goal needs Maximize value of conversions as the ad set performance goal, a working Meta Pixel or Meta SDK tracking conversion events, and eligibility for the Maximize ROAS performance goal (Meta). Meta writes the goal as a ratio: to have a $100 budget bring in about $110 in purchases, you enter 1.100. Google would write that as 110%.

Meta recommends 50 to 100 or more conversions a week for goal-based bidding. With no history, it suggests running Highest volume or Highest value first to set a baseline.

You don't need a paid tool for this. A spreadsheet and three numbers do it: average order value, variable cost per order, and the profit you want left per order.

Gross margin here is (selling price minus variable cost per order) ÷ selling price (Relevant Audience). Break-even ROAS is 1 ÷ gross margin, the same formula Amazon gives in its ads math guide. A 40% margin gives 2.5: you need $2.50 in attributed sales for every $1 of ads to break even, which is 250% in Google's terms.

The CPA side is simpler. Optimize Smart defines max CPA as the most you can pay to win a customer without giving up your operating profit margin, and spending all the profit per customer means breaking even. Our arithmetic from there: break-even CPA is the gross profit on one order, and your max CPA is that minus the profit you want to keep. To move between the two, target ROAS = average order value ÷ max CPA. Optimize Smart's example: a $100 order and a $35 max CPA gives 2.86, about 3.

Never set break-even from revenue. A 2.0 ROAS sounds like doubling your money, but at a 40% gross margin it's below the 2.5 break-even. AdFlint's CPA calculator does the CPA side if you'd rather not do it by hand.

Meta says to set the cost per result goal to the most you're willing to pay per result and the ROAS goal to the lowest ROAS you can accept (Meta), and to base the ROAS goal on the return your business needs to stay profitable (Meta). Google says to set Target ROAS from your business goals, with your historical ROAS as a reference.

Most problems with either strategy come from the number you type in, not from choosing CPA over ROAS.

Google says the renaming started in June 2026, but we found no date for when it reached every account, so yours may still show the old names for a while. Google's Target CPA page gives no minimum conversion count to start (it says you can start with no history); the 30-conversion figure is for evaluating results, not for starting. Meta says a ROAS goal requires eligibility for the Maximize ROAS performance goal, but the help pages we read don't list those rules.

We found no primary Google or Meta source comparing how each platform credits conversions, so this page doesn't compare a Google CPA with a Meta CPA. We left out industry benchmarks: none we found had a named source and date we could check.