What is CPM?
Cost per mille
CPM is what you pay for one thousand impressions of your ad — 'mille' is Latin for thousand.
Formula
CPM = (Spend ÷ Impressions) × 1,000
It's the price of attention, not of results. Buying a thousand impressions tells you nothing about whether anyone clicked, enquired or bought — which is why CPM is a diagnostic number rather than a goal.
Broad consumer audiences on Meta often sit between $5 and $15. Narrow B2B or high-income targeting can run $30–80 or more, because you're competing for a much smaller pool of people. CPM also rises sharply in Q4 as retailers bid up the auction, so a jump in November usually says more about the calendar than about your campaign.
The useful way to read CPM is as an explanation for movements elsewhere. If your cost per lead rose and your CPM rose with it, you're paying more to reach the same people. If your cost per lead rose while CPM stayed flat, the problem is the ad or the offer, not the auction.