What Is CPM in Marketing? CPM, CPC and CPA Side by Side

CPM stands for "cost per mille", mille being Latin for thousand. It is the price an advertiser pays for one thousand impressions, meaning one thousand times an ad is shown. The formula is simple: total cost divided by impressions, multiplied by 1,000. CPM tells you what visibility costs. It says nothing on its own about whether anyone noticed, clicked or bought, which is why it is usually read alongside other measures.

How to calculate CPM

CPM = (total cost ÷ impressions) × 1,000

A made-up example to show the arithmetic: a campaign costs 300 in your currency and the ad is shown 60,000 times. Dividing 300 by 60,000 gives 0.005, and multiplying by 1,000 gives a CPM of 5. In other words, each thousand showings cost 5.

You can also run the formula backwards. If a seller quotes a CPM of 8 and you have 400 to spend, you can expect roughly 50,000 impressions (400 ÷ 8 × 1,000).

The idea is older than online advertising. Newspapers and magazines have long priced space by the number of copies circulated or readers reached, and the same "per thousand" logic carried over to websites, apps and streaming services.

CPM, CPC and CPA compared

CPC vs CPM: which pricing should you choose?

Many ad platforms let you pay either per thousand impressions or per click. The choice depends mainly on what you want the ad to do.

• Pay per impression when the aim is to be seen: announcing an opening, keeping a name familiar before a busy season, or reaching everyone in a small area. If the ad works well and lots of people click, you are not charged extra for that success.
• Pay per click when the aim is a visit: a booking page, an offer, an enquiry form. You only pay when someone shows interest, which limits waste if the ad turns out to be weak.
• Pay per action, where offered, shifts even more risk to the seller but usually comes at a higher unit price and needs reliable tracking.

How the numbers connect

CPM and CPC are linked through click-through rate (CTR), the share of impressions that lead to a click. If you know two of them, you can work out the third:

CPC = CPM ÷ (CTR × 1,000)

Using illustrative numbers again: a CPM of 6 and a CTR of 1% (0.01) gives a CPC of 6 ÷ 10 = 0.60. If the ad is improved and CTR doubles, the effective cost per click halves even though the CPM stays the same. That is why better creative often saves more money than haggling over price.

Carry the chain one step further and conversion rate links CPC to CPA. If one click in twenty turns into a booking, a CPC of 0.60 means each booking costs about 12 in advertising. That figure feeds directly into your overall customer acquisition cost.

What pushes CPM up or down

• Audience size: narrow targeting, such as one postcode and one age group, usually costs more per thousand than a broad audience.
• Demand: busy seasons attract more advertisers competing for the same people.
• Placement and format: prominent spots and video tend to cost more than small banners.
• Quality of the inventory: respected publications can charge more than low-quality sites.

Mistakes to avoid

1. Choosing the cheapest CPM without checking where ads will appear or whether people actually see them.
2. Comparing CPMs across platforms that count an "impression" differently.
3. Ignoring frequency: showing the same ad to the same few people many times inflates impressions without growing reach.
4. Judging an awareness campaign only on clicks, or a sales campaign only on impressions.

Common questions

Is a lower CPM always better?

No. A low CPM on a poorly targeted or barely visible placement can cost more per customer than a higher CPM in front of exactly the right people.

Does CPM apply to print and radio?

Yes. You can divide the cost of a print or radio ad by the outlet's stated readership or listenership and multiply by 1,000 to compare it with online options, keeping in mind that the audience figures are estimates.

Where does CPM fit in planning?

It helps turn a budget into expected reach. Once you know how much to spend on marketing, CPM and CPC quotes show roughly how far that money will go in each channel, which you can then record in your one-page marketing plan.