Cost per lead, explained
Cost per lead (CPL) is the simplest measure of what your marketing buys. Take what you spent on a channel in a period — ad spend, marketplace subscription, agency fees — and divide it by the number of leads that channel produced in the same period. If a month of Meta ads cost 60,000 and brought 300 leads, each lead cost 200.
The number is only as good as the lead count behind it. If some leads are typed in by hand without a source, or duplicates are counted twice, CPL looks better or worse than it is. That is why lead source tracking matters: every lead should keep the channel, campaign and form it came from, so the count per channel is a count, not an estimate.
CPL is also only half the story. A channel with cheap leads that never buy is expensive; a channel with costly leads that close often can be the best money you spend. Compare cost per lead with the share of each channel's leads that become deals, and judge channels on the cost of a customer, not only on the cost of an enquiry.
Recalculate it every month, channel by channel, and watch the trend rather than a single month's figure.