Now that you understand how to measure the impact of your ad campaign, you are ready to start buying some ads. Just like with anything you buy for yourself, you want to make sure you get the best deal. It is just like the old adage, "buy low, sell high." Publishers price their inventory as high as possible to make the most money that they can. The agency tries to negotiate the lowest price possible for the clients so they can buy as many GRPs as possible with the client's budget. But as you have seen, your audience will vary depending on where you place your ad. You can't just compare the price of the ad, you need a way to compare two prices to select the one that is the best deal. The metric that we use to do this is the cost COST PER THOUSAND: the price you pay for every thousand impression. Why do we calculate it based on every thousandth impression? Because we are looking at reaching millions of people so it is easier to look at larger groups of people. CPM = cost of the ad/[total impressions/1000) Example: An ad in People magazine costs $420,000 and reaches 3,400,000 people. The CPM = 420,000/(3,400,000/1000) = $123.53 I might also be thinking about running my campaign in US Weekly, another celebrity/gossip magazine. An ad in US Weekly only costs $307,235, a better deal, right? Well, I'm not sure yet because it depends on how many people will see my ad in US Weekly compared to how many people see my ad in People. I find that there are 1,950,000 readers of US Weekly. Therefore, the CPM is $157.56. Even though the cost of the ad is lower. I'm actuallu nauing more zur zveson I'm reaching In A couple of hints: 1. The term "boy" always means divided by. So if you get confused, cost per thousand will always be the cost of the ad divided by every thousandth impression 2. You can avoid doing the extra calculation of dividing the denominator by 1000 by simply dropping the last three numbers from your impressions number