Formula
CPM = (Spend ÷ Impressions) × 1,000
FAQ
Why did my CPM go up?
Common causes: tighter targeting, more competition (seasonality), smaller audiences, or platform auction changes. Diagnose alongside CTR — a CPM rise with a CTR rise can still be a win.
Is lower CPM always better?
No. Cheap impressions to the wrong audience lose to expensive impressions to the right one. Judge CPM together with downstream CPA/ROAS.