CPA (cost per acquisition)

CPA is what it costs in advertising to win one customer or conversion: total spend divided by conversions.

If $600 of ads produce 12 sign-ups, CPA is $50. Some platforms let you bid on CPA directly and charge per conversion rather than per click.

CPA is only meaningful next to what a customer is worth. A $50 CPA is cheap for a product that earns $300 a customer and ruinous for one that earns $20.