Target CPA vs Target ROAS: Choosing Cost vs Revenue Bidding

Question 1

target cpa vs target roas: what is the practical difference?

Accepted Answer

The article states Target CPA fixes allowable cost per conversion while Target ROAS fixes required revenue per dollar spent. A $15 spatula and a $900 espresso machine both count as one conversion, so a fixed-cost target has no reason to prefer the machine. When every conversion has the same value, the article presents them as two expressions of the same limit; when values differ, they tell the bidding system to favor different clicks.

Question 2

cpa vs roas: how is the bid calculated under each?

Accepted Answer

The article gives simplified calculations for reasoning about the decision. Illustrative bid under Target CPA is predicted conversion rate × target CPA, for example 4% × $100 supports a $4 bid for "commercial boiler repair". Illustrative bid under Target ROAS is (predicted conversion rate × predicted conversion value) ÷ target ROAS, for example 3% × $250 basket is $7.50 expected revenue per click, which supports a $2.50 bid at a 300% ROAS target expressed as 3.0, and only $1.00 if the predicted basket falls to $100.

Question 3

roas vs cpa: when does the article recommend Target CPA?

Accepted Answer

The article recommends Target CPA when conversion values are consistent or cannot be measured reliably. Examples include a single hero product with negligible upsells or a fixed-price offer where there is little for a value model to learn about spend amount. The article states assigned values such as $25 for an ebook, $60 for a form fill, and $200 for a phone call should not be used for ROAS if they are guesses rather than verified revenue.

Question 4

roas and cpa: when does the article recommend Target ROAS?

Accepted Answer

The article recommends Target ROAS when one conversion can be worth far more than another and dynamic transaction values are passed back. Under a $40 Target CPA, $15 spatulas and $900 machines both register as one conversion, which can favor frequent low-value sales. In the article's example at a 300% ROAS target, a $900 expected value at 3% conversion rate supports a $9 bid, while a $25 expected basket at 6% conversion rate supports a $0.50 bid.

Question 5

cpa and roas: how many conversions are needed for Target ROAS to learn?

Accepted Answer

The article states ROAS also asks the system to estimate value if conversion happens, so more variation requires more evidence. The article cites an analysis of more than 14,000 accounts pointing to roughly 50 conversions in a 30-day window as a useful reference for stabilizing Target ROAS, versus roughly 30 for Target CPA. With only 15 or 20 sales a month, the article states one $1,200 checkout does not prove similar queries deserve a much higher bid, and a strict return requirement can leave fewer auctions the bidder can justify entering.

Question 6

Why can cheap conversions shrink revenue under Target CPA?

Accepted Answer

According to groas, a campaign can look healthy on Target CPA while average order value falls because CPA cannot use value in its bid decision. The article gives an $18 accessory converting at 7% and a $650 package converting at 1.4%, with implied CPAs of about $17.14 and $85.71 respectively at a $1.20 click cost. Against a $30 CPA target the accessory looks attractive and the package does not, even though the package may bring far more revenue.