CPA (cost per acquisition)
Spend divided by the number of conversions it produced - the price of an acquired action, attributed to the channel. The channel-level cousin of CAC: CAC reads the whole business, CPA reads one campaign through whatever attribution lens produced it.
Where it's used
Used to steer campaigns in paid search and social. Good for comparing campaigns under one model. Set the target from your margin or LTV.
How to calculate it
CPA = Ad spend ÷ Conversions
Worked example
Illustrative numbersA meal kit brand spends $15,000 on Meta in a month and gets 500 new orders. Each first order earns $22 of margin.
CPA
$15,000 ÷ 500 orders = $30
Loss on the first order
$30 CPA - $22 margin = $8
What it tells you
Losing $8 on the first order is fine only if repeat orders pay it back. CPA alone cannot tell you that, so check LTV.