CPA Calculator

What cost per acquisition means

Cost per acquisition (CPA) is what you pay in advertising, on average, for one conversion: a sale, a sign-up, a lead or a call. Google Ads Help calls a conversion action a specific customer action that you have defined as valuable to your business, such as an online purchase or a phone call (Conversion action: Definition). So the "acquisition" in CPA is whatever you decided to count, and a CPA for newsletter sign-ups and a CPA for purchases are very different numbers.

Google Ads reports the figure as cost per conversion and calculates it by dividing your total cost by the number in the Conversions column (Google Ads Help: Understand your conversion tracking data). Its glossary defines average CPA as the average amount you have been charged for a conversion from your ad (Average CPA: Definition). The formula has three parts, so you can solve for any one of them with the "Solve for" switch.

A worked example

A search campaign cost $600.00, was shown 48,000 times, got 1,200 clicks and brought 36 sign-ups.

• CPA: $600.00 ÷ 36 = $16.67 per sign-up.
• Conversion rate: 36 ÷ 1,200 × 100 = 3% of clicks. CPC: $600.00 ÷ 1,200 = $0.50.
• CTR: 1,200 ÷ 48,000 × 100 = 2.5%. CPM: $600.00 ÷ 48,000 × 1,000 = $12.50.
• At the same CPA, a budget of $1,000 brings about $1,000 ÷ $16.67 = 60.0 conversions.

CPA, CPC and conversion rate are tied together: CPA = CPC ÷ conversion rate, here $0.50 ÷ 0.03 = $16.67. That gives you two levers. A lower cost per click lowers the CPA, and so does a better conversion rate on the landing page, often the cheaper lever to pull. The CTR calculator works one step earlier in the funnel, from impressions to clicks.

Planning with a target CPA

Google Ads Help describes Target CPA as the average amount you would like to pay for a conversion, and notes that some conversions may cost more than your target and some less (About Target CPA bidding). Whether or not you use that bid strategy, a target turns into a plan with three formulas:

For 50 sign-ups at a target of $25.00, you need a budget of 50 × $25.00 = $1,250.00. At the example's 3% conversion rate that takes 1,667 clicks, rounded up, and the clicks may cost up to $25.00 × 0.03 = $0.75 each on average. The CPC calculator uses the same max CPC formula. Since the example campaign pays $0.50 per click, its CPA of $16.67 lands well under the target.

Use a conversion rate from enough clicks to be stable, and from the same kind of traffic you plan to buy. A rate from brand searches will not hold for a cold audience.

Break-even CPA: what a conversion may cost

A target should come from what a conversion is worth to you, not from a number someone else reports. For a sale, the simplest limit is the gross profit of one order:

A $60 order at a 40% margin leaves $24.00 of gross profit. Pay more than that per sale and each one loses money; pay less and the rest is profit. The example's CPA of $16.67 leaves $7.33 per sign-up, or $264.00 across all 36. The profit margin calculator works out your margin if you know price and cost.

Two adjustments make the limit more realistic. If customers come back and buy again, a conversion is worth more than one order, and the customer lifetime value calculator estimates by how much. If a conversion is a lead rather than a sale, multiply the value of a customer by the share of leads that become customers. For whether the campaign as a whole pays off, the ROAS calculator and the marketing ROI calculator look at revenue and profit instead of cost per conversion.

CPA vs CPC vs CAC

• CPC is the cost of one click. It tells you what traffic costs, not what it brings.
• CPA is the ad cost of one conversion. A conversion can be a lead or a trial, not yet a paying customer.
• CAC, customer acquisition cost, divides all sales and marketing costs, including salaries, tools and agencies, by the new customers won. The CAC calculator works it out. It is usually higher than an ad CPA because it carries more costs.

Common mistakes

• Averaging CPAs. $10.00 and $30.00 average $20.00, but with 10 and 30 conversions the real CPA is $1,000.00 ÷ 40 = $25.00. Add up spend and conversions first.
• Counting different things. Google Ads Help explains that the Every setting counts every conversion after an ad interaction, while One counts only one per ad click (About conversion counting options). A CPA from one setting is not comparable with a CPA from the other.
• Mixing date ranges. Spend from one month and conversions from another give a meaningless CPA. Use the same period and the same campaigns.
• Judging small numbers. Three conversions can swing the CPA by a third with one more or one less. Wait for enough conversions before you cut or raise a budget.

How to use the CPA calculator

1. 1Choose what to solve for: the CPA of a campaign that ran, the ad spend for a number of conversions, or the conversions a budget brings.
2. 2Enter the two numbers you know, as totals for the same period from your ad account.
3. 3Add clicks and impressions for conversion rate, CPC, CTR and CPM.
4. 4Enter a target CPA and the conversions you want for the budget, clicks and max CPC, and your order value and margin for the break-even CPA. Copy the result or a link that keeps your numbers.

Built by Tobias Kurth, designer. Updated October 13, 2026.

Frequently asked questions