Ad Calculator
Solve ad cost, CPM, or impressions when two values are known.
About the Ad Calculator
Work out advertising cost from CPM — cost per thousand impressions — which is how display inventory is almost always priced.
How to use it
- Enter the CPM rate.
- Enter the number of impressions.
- Read the total cost.
The formula
CPM is the price of a thousand impressions, which is why the arithmetic always involves dividing by a thousand. The M is the Roman numeral, not 'million' — a surprisingly expensive thing to get wrong.
Cost = CPM × Impressions ÷ 1,000
CPM = Cost ÷ Impressions × 1,000
Impressions = Cost ÷ CPM × 1,000
All three are the same equation rearranged, so knowing any two gives the third. That is what makes CPM useful for comparing quotes: it strips out campaign size and leaves a unit price you can put side by side.
Worked examples
| CPM | Impressions | Cost | Reading |
|---|---|---|---|
| $10.00 | 50,000 | $500 | typical display |
| $25.00 | 50,000 | $1,250 | premium or tightly targeted |
| $10.00 | 250,000 | $2,500 | same rate, five times the reach |
| $4.00 | 1,000,000 | $4,000 | broad, low-intent inventory |
Rows two and four are the trade the whole industry runs on. The same $1,250 buys 50,000 tightly targeted impressions or roughly 312,000 broad ones. Six times the audience for the same money is only a better deal if that audience converts at more than a sixth of the rate — which is why CPM alone never settles the question, and why cost per acquisition is what actually gets judged.
Common mistakes
- Reading the M as million. CPM is cost per thousand, from the Latin mille. Treating it as per-million understates your budget by a factor of a thousand, and it is the single most common error here.
- Comparing CPMs across different placements. A $30 CPM on a trade publication read by buyers and a $3 CPM on untargeted inventory are not comparable numbers. Cheap impressions that never convert are not cheap.
- Confusing impressions with people. One person seeing an ad ten times is ten impressions. Reach counts people, frequency counts how often each saw it, and impressions is the two multiplied together.
- Ignoring viewability. An impression can be counted while the ad sits below the fold and is never seen. Ask what share of impressions are measured as viewable before comparing rates.
Terms explained
- CPM
- Cost per mille — the price of one thousand impressions. The standard unit for buying awareness.
- Impression
- One rendering of an ad. Not one viewer, and not necessarily one that was actually seen.
- Reach
- The number of distinct people exposed at least once.
- Frequency
- The average number of times each person in your reach saw the ad. Impressions divided by reach.
- CPC
- Cost per click — you pay for engagement rather than exposure. Better suited to campaigns with a direct response goal.
- CPA
- Cost per acquisition: what you paid for each actual conversion. The number that decides whether a campaign worked.
Common questions
- What does CPM stand for?
- Cost per mille — mille being Latin for thousand. It is the cost of a thousand impressions, so a $10 CPM buys a thousand impressions for $10.
- Is a lower CPM always better?
- No. Cheap inventory is usually cheap because the audience is broad or the placement is poor. A $25 CPM reaching real buyers can beat a $4 CPM reaching nobody relevant.
- What is a typical CPM?
- It varies enormously by channel and targeting — broad display can run a few dollars, while narrowly targeted professional audiences and premium video run many times that. Compare within a channel, not across.
- How do I work out the CPM I actually paid?
- Divide total cost by impressions delivered, then multiply by a thousand. A $500 spend that delivered 40,000 impressions is a $12.50 effective CPM, regardless of the rate quoted.
- CPM or CPC?
- CPM suits awareness, where being seen is the goal. CPC suits direct response, where you only want to pay when someone acts. CPM shifts performance risk to you; CPC shifts it to the publisher, and is priced accordingly.
- What is a good frequency?
- Enough to be remembered, not enough to irritate. Three to five exposures per person over a campaign is a common target; well beyond that, response typically falls while cost does not.
- Do impressions guarantee anyone saw the ad?
- No. An impression is a served ad. Viewability standards require some portion of the ad to be on screen for a minimum time, and viewable impressions are always fewer than served ones.
- How do I compare a CPM deal to a CPC deal?
- Convert both to the same unit. Estimate the click-through rate on the CPM buy to get an effective cost per click, or estimate impressions on the CPC buy. Then compare like for like.