Formulas
CVR, % = Conversions / Clicks × 100CPA (CPL) = Ad spend / Conversions (leads)CPA = CPC / CVRAd cost per customer = CPL / (Lead → customer %)Maximum allowable cost = Average sale value × MarginCPA and CPL use the same formula — the difference is what counts as a conversion. In e-commerce it is an order (CPA); in service businesses it is often a form, call or message (CPL). A lead is not yet a customer, so the lead-to-sale rate matters too.
Example: a service business
The numbers are hypothetical.
- Monthly spend 1,200, 800 clicks, 40 enquiries (leads).
- CVR = 40 / 800 × 100 = 5%, CPL = 1,200 / 40 = 30.
- 25% of enquiries become contracts → ad cost per customer = 30 / 0.25 = 120.
- Average contract 300, margin 40% → maximum allowable cost = 300 × 0.4 = 120.
The campaign is at break-even: a CPL of 30 looks cheap, but no profit is left per customer. Either lead quality (lead-to-sale rate) or the average deal size must go up.
How to read the result
- If cost per customer is below the allowable limit, the campaign is profitable; if it is above, every new customer comes at a loss.
- A low CVR often points to the landing page rather than the ad: the offer, form length, speed and trust signals.
- Low CPL but few sales — look at lead quality. To measure conversions properly in GA4: marketing KPIs and GA4.
- With repeat purchases, set the allowable limit by customer lifetime value rather than a single sale.
Common mistakes
- Treating every conversion the same. A page view or a click on the call button is not a sale. CPA should use conversions that matter to the business.
- Counting leads as customers. Presenting CPL as customer acquisition cost makes results look better than they are.
- Adding up platform conversions. If Google and Meta both count the same lead, the total exceeds reality.
- Deciding on a small sample. With 3–5 conversions CPA swings randomly; collect more data before deciding.
Frequently asked questions
What is CPA?
CPA (cost per acquisition) is the average ad cost of one conversion: spend divided by conversions. 20 orders for 1,000 in spend means a CPA of 50.
What is the difference between CPA and CPL?
The formula is the same; the conversion differs: CPA usually refers to a sale or order, CPL to an enquiry (form, call, message). Because a lead is not yet a customer, CPL is lower than cost per customer.
How is conversion rate calculated?
CVR = conversions / clicks × 100. 15 conversions from 500 clicks is a CVR of 3%. GA4 also uses session-based rates — always state which denominator you use.
How do I set a maximum CPA?
At the profit one customer brings: average sale value × margin. With an average order of 200 and a 30% margin, more than 60 in ad cost per customer loses money.
Can conversions exceed clicks?
Yes: several conversions can be counted per click, or the platform may include view-through conversions. Check which column the report uses.
Are my numbers sent anywhere?
No. The calculation runs in your browser. The result is only sent to ClickOptimize if you submit the "Send the result to an expert" form yourself.