Two questions come up in every media plan. How much do I need to spend to reach this many people? And how much do I need to spend to get this many sales? Both are simple multiplication once you fix four numbers: the size of the audience, the CPM, the frequency you plan for, and your click and conversion rates.
The calculator below does both. Change any number and the answer updates. Nothing leaves your browser, and nothing is stored.
The shared inputs
CPM is what you pay for 1,000 impressions. Use your own recent average for the audience type you are buying.
A. Spend needed to reach an audience
Impressions needed = audience × reach × frequency. Spend = impressions ÷ 1,000 × CPM.
B. Spend needed to hit a conversion goal
Impressions needed = conversions ÷ (link CTR × conversion rate). The same CPM then turns that into spend.
How to read the answers
Why the reach answer is a floor
The formula assumes every impression goes to a fresh pair of eyes up to your frequency target. Real delivery does not work that way. Some people see the ad far more often than average while others never see it, and the last slice of an audience is the most expensive to find. CPM also rises as you push towards the edge of a pool, so one fixed number understates the cost of high reach. Ads Manager's own audience size figure is an estimate, which adds another layer of slack. Use the result to size a plan, then compare it with the delivery estimates in the platform before you commit.
Frequency is a planning input, not a threshold
The frequency box asks how often you intend people to see the ad. It does not say 3 is correct. The largest public study of frequency effects, Randall Lewis's analysis of 2.8 billion display impressions across 30 campaigns, found no single curve: a third of campaigns showed no wear-out at all, and the rest ranged from near-linear returns to steep decay. Set frequency from your own account history. We cover the study in what frequency actually does to CTR.
The conversion goal tells you whether the plan is viable
Calculator B works backwards from the outcome, and the implied cost per conversion is the number to check first. It is simply the CPM divided by 1,000 times the click and conversion rates. If your CPM is €12, your CTR is 1% and your conversion rate is 2%, every sale costs about €60 before anything else. Doubling the conversion rate halves that cost as surely as halving the CPM does, and creative is the lever that moves click rate. In NCSolutions' analysis of nearly 450 CPG campaigns, creative accounted for 49% of sales impact. It is CPG data, so take it as direction rather than a constant. See Creative is 49% of the outcome.
It does not model diminishing returns, seasonality, auction competition or the lag between seeing an ad and buying. It also takes your conversion rate as given, when in practice it changes with the offer and the audience. It answers "what does this plan cost if my assumptions hold", which is the first question and rarely the last.
The inputs above are the ones teams guess at. Knack reads your actual CPM, CTR, conversion rate and frequency by creative from the connected account, and grades each ad against the metric its campaign objective implies. Once you know what your plan costs, the useful next question is which creative earns it back. Try the sister tool: how many creatives can your budget test.
Sources and method
- Spend = impressions ÷ 1,000 × CPM. Impressions = audience × reach × frequency, or conversions ÷ (CTR × conversion rate). These are accounting identities, not estimates.
- Lewis, R. A. Worn-Out or Just Getting Started? The Impact of Frequency in Online Display Advertising. Display advertising, so take the structure of the finding, not the coefficients.
- NCSolutions sales driver analysis of nearly 450 CPG campaigns, reported by MarketingCharts.