What is CPA (cost per acquisition)?
CPA, or cost per acquisition, is the average amount you spend on advertising to get one conversion. A conversion is whatever action you define as valuable: a purchase, an app install, a lead form or a sign-up. CPA is calculated by dividing total ad spend by the number of conversions, and it is one of the most common performance metrics in digital advertising.
CPA can be a reporting metric, a bidding goal or, less often, a pricing model where the advertiser pays only when a conversion happens.
How is CPA calculated?
CPA = total ad spend / number of conversions
For example, if a campaign spends $2,000 and drives 80 sign-ups, the CPA is $2,000 / 80 = $25. If you lower spend on weak placements and still get 80 sign-ups for $1,600, your CPA drops to $20.
CPA connects to other pricing metrics. If you buy on a CPM basis, CPA depends on how many impressions it takes to produce a conversion. At a $5 CPM, 1,000,000 impressions cost $5,000. If those impressions drive 200 purchases, the CPA is $25.
Why CPA matters
Clear efficiency signal: CPA tells you what each result costs, which is easy to compare against what a customer is worth.
Bidding target: most DSPs offer automated bidding that aims for a target CPA, adjusting bids by the likelihood of conversion.
Budget planning: if you know your acceptable CPA and conversion goal, you can work back to the budget you need.
CPA has limits. It depends on how conversions are tracked and credited, so the attribution window and model matter. A last-click view may undervalue display and video that started the journey, which is where multi-touch attribution and incrementality testing help. CPA also treats every conversion as equal, even when some customers are worth far more than others.
CPA vs ROAS
CPA measures cost per result. ROAS (return on ad spend) measures revenue per dollar spent. If every conversion has a similar value, such as a fixed-price subscription or a lead, CPA is usually the simpler goal. If order values vary a lot, as in ecommerce, ROAS gives a better picture, because a $25 CPA on a $40 order and a $25 CPA on a $400 order are very different outcomes.
How to lower CPA
Tighten audiences toward people with higher intent, such as site visitors or in-market segments.
Cut placements and exchanges with high spend and no conversions.
Test creative and landing pages, since conversion rate drives CPA as much as media cost.
Give automated bidding enough conversion data and time before changing targets.
CPA with AdGeeks
AdGeeks traders set up conversion tracking and CPA-based bidding on DV360, Amazon DSP and Adform, then optimize placements, audiences and bids against your target. Reporting shows CPA by line item and supply source, so you see where results come from. To get started, request access.
