Metrics
CPA
Cost per acquisition — ad spend divided by conversions.
CPA (cost per acquisition) is what it costs you to produce one paying conversion. It is ad spend divided by conversion count. Operators bid by CPA target on most platforms (tCPA on Google Ads, target CPA on Meta, manual CPA bidding on Taboola Smart Bid). Your breakeven CPA equals AOV × gross margin: bid above that and you bleed.
Formula
CPA = ad spend / conversions
Example
Spent $4,000 on Outbrain, got 80 sales. CPA = $50. AOV is $99 and margin is 55%, so breakeven CPA is ~$54 — campaign is profitable but tight.