CPM (Cost Per Thousand)
CPM = (Spend ÷ Impressions) × 1,000. In email, you see it when buying sponsorship slots or renting a list.
CPM (Cost Per Thousand, also Cost Per Mille, where “mille” is Latin for thousand) is the price of reaching 1,000 people with a message. In email you meet it when buying a newsletter sponsorship, renting a list, or paying for placement in someone else’s send.
CPM = (Total Spend ÷ Total Impressions) × 1,000
A hypothetical example: a $500 sponsorship slot in a newsletter delivered to 25,000 subscribers works out to a $20 CPM. Whether that is a fair price depends on what an “impression” means in the deal. Some sellers count delivered emails, others count opens, and the two numbers can differ a lot. Ask which one the rate is based on before comparing offers.
CPM is a reach price, not a result. To judge a placement, pair it with what happened afterward: clicks (click-through rate), signups or purchases (conversion rate), and what those cost per outcome. Two sponsorships with the same CPM can produce very different results if one audience fits your product and the other does not.
Common mistakes
Comparing CPMs across placements without checking how impressions are counted, and treating a delivered email as a seen one. Open rate is an imperfect proxy for either.