Cost Per Acquisition
The total cost required to acquire one converting customer, calculated by dividing total campaign spend by the number of conversions attributed to that campaign.
Cost per acquisition (CPA) is the primary efficiency metric for paid acquisition — and it's directly improved by conversion rate optimization. For every dollar spent on media, CPA tells you how many dollars it cost to generate one customer. Lower CPA means either you're spending less for the same volume of customers, or acquiring more customers for the same spend.
The CRO Lever on CPA
CPA is a function of two variables: media cost (CPM or CPC) and conversion rate. CRO directly attacks the second variable. If your CPA is $80 and your landing page conversion rate is 2%, a successful test that raises conversion rate to 2.5% drops your CPA to $64 — a 20% efficiency gain with no change in media spend. This is why high-traffic paid channels are prime candidates for A/B testing investment.
CPA vs. CAC: Understanding the Distinction
CPA and customer acquisition cost (CAC) are related but not identical. CPA is typically calculated per campaign or channel and may count any defined conversion event (including micro-conversions like lead form fills). CAC is a business-level metric that includes all sales and marketing costs divided by total new customers acquired. CPA is an optimization metric; CAC is a business health metric. Confusing them leads to reporting errors and misaligned incentives.
Target CPA and Bidding Strategy
In Google Ads and Meta, target CPA bidding allows platforms to automatically allocate spend toward users most likely to convert at or below your target CPA. Setting this target correctly requires knowing your CLV and acceptable payback period. A/B testing landing pages while running target CPA bidding requires careful experiment design: traffic allocation must be balanced across variants at the ad group level to avoid bid strategy interference.