In media buying, CPM stands for cost per mille, where mille is Latin for 1,000. It represents the cost of 1,000 impressions, or views, of an advertisement. If you know your desired number of impressions and the CPM, you can calculate your budget using the following formula: Budget = (Number of Impressions / 1000) x CPM For example, if you want to achieve 500,000 impressions with a CPM of $2, your budget should be (500,000 / 1,000) x $2 = $1,000.