Cost per mille (CPM) is the price an advertiser pays for one thousand ad impressions, where “mille” is Latin for thousand. It measures the cost of reach, not clicks or sales, so it tells you how expensive it is to get your ad shown, regardless of what people do next. CPM is the standard way to compare the raw price of exposure across channels like Meta, Google Display, LinkedIn, and programmatic buys.
How it works
The formula is simple: CPM equals total spend divided by impressions, multiplied by 1,000. If you spend 500 dollars and get 250,000 impressions, your CPM is 2 dollars. Some platforms let you buy on a CPM basis directly (you pay per thousand views), while others report CPM as a derived metric even when you are actually bidding on clicks or conversions.
Why it matters
CPM is useful for judging the efficiency of awareness and reach campaigns, and for spotting when a channel or audience is getting expensive. A rising CPM often signals more competition for the same audience or a shrinking, over-targeted segment. On its own, though, CPM says nothing about quality. A cheap CPM that reaches the wrong people is worse than a higher CPM that reaches qualified buyers.
Example in B2B
B2B audiences are small and specific, so CPMs on platforms like LinkedIn run far higher than broad consumer reach on Meta. A wholesale supplier targeting procurement managers might accept a 40 dollar CPM because the buyers are worth large, repeat orders. What matters is not the CPM alone but the downstream value: how many of those impressions become quote requests, and how many quotes convert to paid orders.
For Shopify merchants running B2B, that means tracking cost per impression alongside what happens after the click. If you route inbound interest into quote requests, connecting ad spend to accepted quotes gives CPM context it lacks by itself. See the B2B quoting glossary for related terms.