How to calculate CPE
Divide the amount spent by the count of engagements you decided to include. A campaign costing $500 with 250 counted interactions has a cost per engagement of $2. This arithmetic is simple; the important judgment is what the numerator and denominator contain.
Define an engagement first
A platform may count clicks, video interactions, reactions, or other actions differently. Google Ads says its average CPE is the average amount charged for an ad engagement and provides a separate engagement-rate metric. A cross-platform calculation using your own spend and count may therefore differ from a platform-reported average. Record the exact event definition and whether the spend includes agency fees, production, or only media charges.
Compare like with like
Use the same reporting period, currency, platform, and attribution rules when comparing campaigns. A lower CPE is not automatically better: a cheap interaction from the wrong audience may be less useful than a more expensive qualified visit or inquiry. Track the subsequent outcomes that match your objective, and do not combine unlike interactions into one total without explaining the mix.