How to use the CPA calculator
Enter ad spend for the period.
Enter conversions: purchases, sign-ups or leads, whichever the campaign optimizes for.
Add your target CPA. If you sell products, the break-even ROAS calculator gives you the maximum CPA.
Optionally add average order value to see the ROAS this CPA implies.
The CPA formula
- CPA=ad spend ÷ conversions
- Implied ROAS=average order value ÷ CPA
- Conversions needed at target=ad spend ÷ target CPA
- CPA=CPM ÷ (1,000 × CTR × conversion rate)
- Conversions
- Results counted for the campaign. Count the event you care about, not a proxy such as add to cart.
- Target CPA
- The most you are willing to pay per conversion, usually derived from margin or customer value.
- Average order value
- Average revenue per order, excluding tax.
Worked example
A campaign checked against target
- Spend 3,000 for 84 purchases: CPA = 3,000 ÷ 84 = 35.71.
- Target CPA is 40, so the campaign is 10.7% under target.
- Average order value is 65: implied ROAS = 65 ÷ 35.71 = 1.82x.
- At target CPA, the same spend would only need 3,000 ÷ 40 = 75 purchases.
Setting a target CPA
Start from economics, not from what feels cheap. For a one-off purchase the ceiling is your contribution per order: price minus product, shipping and fees. If customers buy repeatedly, you can justify a higher CPA based on gross profit over a realistic period such as 90 or 180 days.
For lead generation, work backwards: target cost per lead = profit per customer × lead-to-customer rate. A lead that closes 10% of the time on 1,000 of profit is worth at most 100.
CPA across the funnel
CPA breaks down into three levers: CPA = CPM ÷ (1,000 × CTR × conversion rate). When CPA is too high, find the weak lever before changing everything at once.
- High CPM: the audience or season is expensive, or the ad is judged low quality.
- Low CTR: the hook, offer or creative is not stopping the scroll.
- Low conversion rate: the landing page, price or offer is not closing the people who click.
Reading CPA honestly
Ads Manager reports CPA using attributed conversions, and small samples are noisy. A campaign with six purchases can swing wildly from one day to the next. Wait for enough conversions before cutting or scaling, and read the trend over several days rather than a single one.
- Compare CPA with the same attribution setting across periods.
- Use first-time customer CPA if you can; returning customers are cheaper and flatter the number.
- Expect CPA to rise somewhat after budget increases, and decide in advance how much rise you will accept.
Questions and answers
What is CPA in advertising?+
Cost per acquisition, also called cost per action or cost per result: ad spend divided by the number of conversions.
How do you calculate CPA?+
Divide total ad spend by conversions. 1,500 spent for 50 sales is a CPA of 30.
What is a good CPA?+
Any CPA below the maximum your economics allow. For ecommerce that is usually your contribution per order, or a higher figure justified by repeat purchases. Industry averages are rarely useful because order values and margins vary so much.
What is the difference between CPA and CAC?+
CPA usually refers to one campaign or channel and one action. CAC, customer acquisition cost, is broader: all sales and marketing costs divided by new customers. CAC is typically higher than any single campaign's CPA.
How is CPA related to ROAS?+
For purchases they are two views of the same thing: ROAS = average order value ÷ CPA. A 60 order at a 20 CPA is a 3x ROAS.
How many conversions do I need before trusting CPA?+
More is better. Meta's own guidance is about 50 optimization events per ad set within a week to exit the learning phase, which is a sensible bar before drawing firm conclusions. With only a handful of conversions, judge the trend over a longer window.