CPL (cost per lead) is the amount of advertising spend required to obtain one lead.
CPL = ad spend ÷ number of leadsIf a campaign spends €1,000 and produces 80 leads, the CPL is €12.50.
Why the definition hides the hard part
The formula is trivial. What is not trivial is deciding which spend and which leads go into it:
- Which spend. Campaign spend is an average across every ad inside it. Spend per
ad_idis the granular number, and it is the one that lets you act. - Which leads. A lead counted by the ad platform (attributed through its own model, after iOS restrictions) and a lead counted by your own tracking (a click you logged and a form you received) are two different numbers. They never match exactly.
Which number to trust
DropCPL treats the first-party count as the ground truth: a click logged on the tracking domain, a cookie set server-side, a form submission received. It is deterministic, so it is reproducible.
The platform-reported conversion is still sent back to Meta through the Conversions API, because Meta’s optimizer needs it. But it does not define the CPL shown in the product.
Two truths, one canonical. Averaging them would produce a number that is precise about nothing.
Related terms
- Real CPL — the first-party number, as opposed to the platform one
- CPA — the downstream cost of a customer
- Attribution window — how long after a click a lead still counts
- CPL vs CPQL calculator — run the two numbers on your own campaigns