CPM Calculator

What is CPM, and the two questions it answers

CPM is cost per mille: what you pay for a thousand impressions. Because the formula ties three numbers together, knowing any two gives you the third. That is why this calculator solves in all three directions.

• CPM from cost and impressions €4,000 for 500,000 impressions is a CPM of €8.00. This is the question you ask when comparing two quotes that are not priced the same way.
• Impressions from budget and CPM €1,200 at a €6.00 CPM buys 200,000 impressions. This is the one to run before a negotiation, because it converts a price into reach.
• Cost from impressions and CPM 250,000 impressions at a €3.40 CPM costs €850.00. This is how you build a media plan backwards from a reach target.

CPM against CPC, CPA and ROAS

CPM prices attention, not action. You pay for the impression whether or not anyone clicks, which makes it the right buy for awareness, a launch, a brand campaign, anything where being seen by the right audience is the point, and the wrong buy for direct response unless you already know your rates downstream.

The chain is worth holding in your head: impressions × click-through rate = clicks, and cost ÷ clicks = CPC. A €8.00 CPM with a 0.5% CTR is a €1.60 effective cost per click; the same €8.00 CPM at 0.1% is €8.00 a click, and the same inventory has gone from cheap to expensive without the price changing. One step further, clicks × conversion rate gives conversions, and cost ÷ conversions is your CPA, which is the number a performance campaign actually lives or dies by. Compare CPMs only within the same format and audience: a €15 CPM on a targeted newsletter and a €2 CPM on run-of-network display are not comparable rates, they are different products.

Building and checking a media plan

A plan is a list of line items, and the useful check is whether the totals come out where you expected. Switch to bulk mode, drop in a CSV of line items, a name plus any two of cost, impressions and CPM, and each row is solved for the missing value, with the blended totals at the bottom.

The blended CPM is the number worth looking at hardest, because it is not the average of the row CPMs: it is total cost ÷ total impressions × 1000, so a single large cheap placement pulls it down more than a small expensive one pushes it up. Rows with fewer than two values are flagged rather than guessed at, the delimiter is detected so an Italian or German Excel export works unchanged, and 3,4 is read as 3.4 so a decimal comma does not silently become a number thirty times too big. Copy the table or download it as a CSV to attach to the plan.

What CPM hides

• Impressions are not people frequency is impressions ÷ reach. A million impressions at a frequency of ten is a hundred thousand people seeing the ad ten times, which is a different campaign from a million people seeing it once.
• Viewability an impression can be counted while the ad is below the fold and never seen. A low CPM on low-viewability inventory can cost more per viewable impression than a higher published rate, so ask for vCPM.
• Invalid traffic bot impressions are impressions as far as a CPM is concerned. On open exchanges ask what share is filtered and whether you pay for it.
• Fees a platform fee, an ad-serving fee and an agency fee all sit between your budget and the publisher. Work out whether the CPM you were quoted is gross or net, because the two can be twenty per cent apart.