The formula, without the mystery.
Visitors = target sales / conversion; ad spend = visitors × paid share × CPC
A worked example
At a 2% conversion rate, 200 sales need 10,000 expected visitors. If 30% are paid at 0.50 per click, expected advertising spend is 1,500.
Can I use clicks and sessions interchangeably?
Only if your measurement is consistent. This model assumes each paid click produces a counted visitor. Adjust effective CPC if clicks are lost before arrival.
Keep the assumptions consistent
Use one planning period and one currency. Enter amounts consistently excluding sales tax or VAT. These simplified models do not account for uncertainty, inventory limits, working capital or progressive taxes. Results are planning estimates.