Required Ad Impressions Calculator
Written by Thierno Sadou Diallo, formula verified per our methodology • Last checked on 9/10/2026
The number of required impressions is calculated with target conversions ÷ (click-through rate × conversion rate). For 100 target conversions with a 2% CTR and a 5% CVR, you need 100,000 impressions, about €800 at an €8 CPM.
Explanation
Planning an ad campaign means working the conversion funnel backwards: from a results goal (sales, sign-ups, contact requests), you derive how many clicks you need to generate, then how many impressions you need to buy to get those clicks. The calculation relies on two rates measured from past campaigns: the click-through rate (CTR), the share of people who saw the ad and clicked, and the conversion rate (CVR), the share of those visitors who complete the target action once on the site. This calculator reverses the logic of our CPM and CPC calculator, which computes unit costs from known volumes, and of our marketing conversion rate calculator, which measures a rate from volumes: here, you start from the goal to size the media buy and estimate the budget. The result's reliability depends entirely on the accuracy of the rates entered: an overly optimistic CTR or CVR estimate heavily under-sizes the actual budget, because the two rates multiply (halving both CTR and CVR quadruples the number of impressions needed). It's therefore wise to test the campaign on a small volume to measure the actual rates before committing the full budget.
Example: 100 target conversions, 2% CTR, 5% CVR
Inputs
Target conversions: 100. Click-through rate: 2%. Conversion rate: 5%. CPM: €8.
Calculation
Clicks needed = 100 ÷ 5% = 2,000. Impressions needed = 100 ÷ (2% × 5%) = 100 ÷ 0.001 = 100,000. Budget = 100,000 ÷ 1,000 × 8 = €800.
Result
To get 100 conversions, you need to buy about 100,000 impressions (2,000 expected clicks), for a budget of about €800.
Frequently asked questions
Why does a small error in the rates change the result so much?
Because the click-through rate and conversion rate multiply in the calculation: if both are half of what was expected, the number of impressions needed isn't doubled but quadrupled. An optimistic estimate of both rates at once can therefore lead to an actual budget two to four times higher than planned — hence the value of testing before committing the whole amount.
Where do I find my actual click-through and conversion rates?
The click-through rate (CTR) is provided directly by the advertising platform (Google Ads, Meta, etc.) in the campaign report. The conversion rate (CVR) is measured on your site using an analytics tool configured to track the target action (purchase, form submitted). Without your own data, published industry averages give an order of magnitude, to be treated with caution as they vary widely by sector and ad format.
Is the CPM used for the budget fixed?
No, the cost per thousand impressions (CPM) varies with the platform, targeting, seasonality, and competition for the target audience: a niche audience or a high-demand period (year-end holidays) drives the CPM up. The budget estimated by this calculator assumes a constant CPM: in reality, you should allow a margin and adjust during the campaign based on the CPM actually observed.