Cost Per Lead (CPL)
CPL doesn't answer how much a lead costs. It answers how much something you've decided to call a 'lead' costs, which makes the metric useful only if that definition is the same in every comparison.
“Two channels with the same CPL can cost twice as much as each other, if one of them calls 'lead' something the other would call noise.”
Otto GTM ObservatoryThe problem isn't the cost, it's the definition
CPL is only useful when the lead definition underlying the calculation remains identical over time and across channels: same set of qualification criteria, same minimum information threshold, same verification process. Without this discipline, CPL becomes an easily manipulated metric by implicitly lowering qualification standards to make a channel appear more efficient than it really is.
A low CPL obtained on leads that rarely convert into real opportunities simply shifts the cost of inefficiency from the media budget to the sales team's time spent manually qualifying them, a cost often higher and less visible than CPL itself.
Anti-patterns
Common mistake: comparing CPL between different channels (e.g. LinkedIn Lead Gen Forms vs. gated content on the site) without verifying the qualification criterion applied is identical, reaching unfounded relative efficiency conclusions.
Second mistake: aggressively optimizing to reduce CPL by lowering the minimum information threshold required, getting a metric improvement paired with a worsening lead-to-opportunity conversion rate downstream.
Practical Application
A company compares a €42 CPL on LinkedIn Lead Gen Forms (only name and email required) versus a €118 CPL on a gated whitepaper with 6 qualifying fields. The lead-to-opportunity conversion rate is 3% for the first channel and 24% for the second: the real cost per qualified opportunity is €1,400 for LinkedIn versus €492 for the whitepaper, reversing the conclusion suggested by CPL alone.