How to calculate CPA
The formula is CPA = total ad spend / number of conversions. A Google Ads campaign that spent $3,000 and produced 60 booked estimates has a CPA of $50. The number only means something if the conversion is defined tightly: a CPA built on clicks to the contact page will always look better than one built on submitted forms or answered calls.
In Google Ads, the Cost / conv. column runs this calculation for every campaign, ad group and keyword. Check the counting setting first: count One conversion per click for leads and Every conversion for ecommerce purchases. With Every on a lead gen campaign, a visitor who submits two forms cuts your reported CPA in half.
What is your maximum CPA?
A healthy CPA comes from your unit economics, not from an industry average. For a direct sale, breakeven CPA equals the gross profit on that sale. For a lead, factor in your close rate: maximum CPA per lead = gross profit per customer × close rate.
Example: a roofing contractor in Dallas earns $4,000 in gross profit per job and closes one estimate in five. Each lead can cost up to $800 before the job stops making money. Targeting $300 to $400 per lead leaves room for estimator time, callbacks and the jobs that never close.
Mistakes that distort CPA
Never read CPA in isolation: $25 on 4 conversions a month is often worth less than $40 on 60 conversions if your margin allows it. Also watch for these common traps:
- Mixing primary conversions (quote, purchase) with secondary ones (phone number clicks, downloads) in the same column.
- Making decisions after one week or fewer than 30 conversions, while variance is still high.
- Blending cheap branded campaigns with expensive non-branded ones into an average that describes neither.
- Ignoring offline sales: a lead that signs three weeks later must be imported, or your CPA measures form fills instead of customers.
