What this calculator does
Cost per acquisition is the average amount spent to win one conversion, usually a sale, sign-up or other action that counts as a genuine business result rather than just a click. It is the figure that connects ad spend directly to the outcome that actually matters.
CPA is only meaningful alongside what that acquisition is worth. A $50 CPA is a bargain if the customer is worth $500 over their lifetime, and a poor result if the product sells for $40. CPA tells you what something cost, not whether it was worth it.
The formula
Divide total ad spend by the number of conversions it generated. The result is the average cost of winning one conversion over that spend.
| Term | Meaning |
|---|---|
| CPA | Cost per acquisition: total spend ÷ number of conversions. |
| Conversions | Completed sales, sign-ups or other actions counted as a successful outcome. |
| Spend | The total amount spent to generate those conversions. |
The inputs explained
| Field | What to enter |
|---|---|
| Total ad spend ($) | The total ad spend over the period being measured. |
| Conversions (sales or sign-ups) | The number of conversions (sales or sign-ups) that spend produced. |
When to use it
Judging whether a campaign is profitable
Comparing CPA against the value of a typical customer is the most direct profitability check available for a paid campaign.
Setting a maximum acceptable bid
Knowing the CPA a campaign can sustain and stay profitable sets a ceiling on how aggressively to bid for clicks or impressions.
Comparing acquisition channels
Different channels (search, social, affiliate) often deliver very different CPAs for the same product, which helps decide where to reallocate budget.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How CPA changes as spend increases at a fixed number of conversions
A fixed 40 conversions, at a range of total spend levels.
| Total spend | CPA | Conversions per $1,000 spend |
|---|---|---|
| $1,000 | $25.00 | 40.00 |
| $2,000 | $50.00 | 20.00 |
| $3,000 | $75.00 | 13.33 |
| $4,000 | $100.00 | 10.00 |
| $6,000 | $150.00 | 6.67 |
| $8,000 | $200.00 | 5.00 |
How CPA changes as conversions increase at a fixed spend
A fixed $2,000 budget, across a range of conversion counts.
| Conversions generated | CPA | Conversions per $1,000 spend |
|---|---|---|
| 10 | $200.00 | 5.00 |
| 20 | $100.00 | 10.00 |
| 40 | $50.00 | 20.00 |
| 60 | $33.33 | 30.00 |
| 80 | $25.00 | 40.00 |
| 100 | $20.00 | 50.00 |
Questions
What is a good CPA?
It depends entirely on what a customer is worth to the business, which varies by product, margin and repeat-purchase behaviour. The relevant comparison is CPA against customer value, not CPA against an industry average.
How is CPA different from CPL?
CPA usually measures the cost of a completed sale or paying customer, while CPL (cost per lead) measures the cost of an earlier-stage contact, such as a form fill, that has not yet become a paying customer.
Why is CPA higher on some channels than others?
Channels differ in audience intent and competition. A channel that reaches people already looking to buy typically converts more efficiently, and therefore posts a lower CPA, than one reaching a colder audience.
Should I aim to minimise CPA at all costs?
Not in isolation. Pushing CPA down aggressively can mean cutting volume or targeting only the easiest conversions, which can shrink overall growth even as the average cost per sale falls.
To compare cost against revenue rather than conversions alone, see the ROAS calculator. For the cost of an earlier-stage lead rather than a completed sale, see the CPL calculator.