What CPA means
CPA stands for cost per acquisition. It is the amount of ad spend it took to produce one conversion, whether that conversion is a sale, a signup, or a lead. The formula is short:
CPA = ad spend / conversions
Spend $800 on a campaign that produces 40 conversions and your CPA is $20. Each conversion cost you $20 in ad spend. It is the cleanest way to compare ad sets and campaigns against each other, because it strips out the size of the budget and leaves you with a per-result price.
How to read your CPA
CPA only means something next to your profit per order. If you earn $25 of profit on each sale, a $20 CPA leaves you $5 ahead. A $30 CPA puts you $5 behind. So the question is never "is this CPA low?" in the abstract, it is "is this CPA below my profit per order?"
That makes CPA a fast campaign-level filter:
- CPA below profit per order: the campaign makes money. Scale it.
- CPA at profit per order: you are breaking even. Useful for acquiring customers you expect to buy again.
- CPA above profit per order: the campaign loses money on the first sale. Justify it only if repeat purchases make up the difference.
For the full-funnel view across every channel, switch to CAC. To check the same campaign as a ratio, use the ROAS calculator.
A worked example
A campaign runs for a week:
- Ad spend: $1,200
- Conversions: 48
- CPA = 1,200 / 48 = $25
Each sale cost $25 to acquire. If your product leaves $35 of profit after costs, you are making $10 per order and should push more budget in. If it leaves $20, you are losing $5 a sale and need to fix the offer or the targeting.
Feed the calculator with real numbers
Sizing a competitor's campaign means knowing what they sell and for how much. Koala Inspector is the Chrome extension media buyers use to see the live ads, best-selling products, and pricing on any Shopify store, so you can estimate the economics of a niche before you spend. Compare tools in our Shopify spy tools list.
