Ad cost calculator: CPC, CPM and CPA
Ad spend is easy to increase. Knowing whether the increase is working is harder. CPC, CPM and CPA are the three numbers that tell you what you actually paid: per click, per thousand impressions and per conversion.
Enter your campaign numbers once and see whichever metrics you have data for.
- Ad cost calculator
- CPC, CPM and CPA: what they measure
- Why your CPA is only as good as your tracking
- How to track ad conversions in Plausible
Ad cost calculator
CPC, CPM and CPA: what they measure
Cost per click, or CPC, is what you paid for each visitor an ad sent to your site. It is the right metric when the click itself is the goal, or when comparing campaigns on the same channel. It says nothing about what happens after the click. Formula: ad spend divided by clicks.
Cost per mille, or CPM, is what you paid per thousand impressions. It is a reach metric, not a performance metric. A low CPM means your ad is being shown cheaply. Whether anyone clicks or converts is a separate question. Formula: ad spend divided by impressions, multiplied by 1,000.
Cost per acquisition, or CPA, is what you paid to get one conversion. Whether that is a sale, a signup or a lead depends on how you define it. CPA is the metric that most directly links spend to business outcome, which also makes it the one most exposed to bad data. Formula: ad spend divided by conversions.
In practice you need all three. A strong CPC with a bad CPA means clicks are cheap but the landing experience is failing. A low CPM with no conversion tracking is just cheap reach with no proof of return.
When you have enough data, the calculator also surfaces two derived metrics. Click-through rate (clicks divided by impressions) tells you what share of people who saw the ad actually clicked it. Conversion rate (conversions divided by clicks) tells you what share of those clicks turned into something useful. A high CPC paired with a strong conversion rate can still be profitable. A cheap CPC with a near-zero conversion rate is not.
Why your CPA is only as good as your tracking
CPA divides spend by conversions. The spend number is exact. The conversion number often is not.
Cookie consent banners cause some visitors to decline tracking. When that happens, Google Analytics does not record the conversion. The visitor came, converted and left no trace. Your conversion count shrinks, your CPA goes up, and the campaign looks less efficient than it actually was. Our cookie banner traffic loss calculator can help you estimate the size of that gap.
Ad blockers strip tracking scripts. For audiences that skew technical, the gap between actual and recorded conversions can be significant.
Plausible tracks conversions without cookies, so it does not require consent to record a goal completion. The result is a more complete conversion count to feed into your CPA calculation.
This does not mean replacing your ad platform’s conversion signal entirely. Platforms need that signal for optimisation. But Plausible gives you an independent count less subject to consent drop-off, so you can check whether the platform’s numbers are in the right range.
How to track ad conversions in Plausible
To connect ad spend to conversion data in Plausible, you need goals set up in your dashboard and UTM parameters in your ad URLs.
Set up goals: Define what counts as a conversion. Pageview goals work without any code if the conversion results in a page load, such as a /thank-you URL. For button clicks and other interactions that do not change the URL, custom event goals let you track those with a small snippet. For form submissions, Plausible has automated form submission tracking that requires no custom code at all.
Tag your ad URLs: Add utm_source, utm_medium and utm_campaign parameters to every ad URL. Use the UTM builder to generate clean, consistent URLs, or the UTM checker to validate existing tags before they fragment your campaign data. Plausible captures these parameters automatically and breaks down goal completions by campaign, so you can calculate CPA per campaign directly from your dashboard without relying on the ad platform’s attribution model.
Add revenue tracking: If your conversions have a monetary value, ecommerce revenue tracking lets you record the value alongside each conversion. This lets you compare revenue against spend per campaign rather than just counting conversions.
