A conversion is a visitor action that the ad platform counts as success: a purchase, a submitted lead or a phone call. For an online store the primary conversion should be a completed purchase with the order value, not an add-to-cart. Automated bidding learns from conversions, so whatever you count is what the system goes looking for.
A conversion is a visitor action that the ad platform counts as success: a purchase, a submitted lead or a phone call. For an online store the primary conversion should be a completed purchase with the order value, not an add-to-cart. Automated bidding learns from conversions, so whatever you count is what the system goes looking for.
Every other number in the account is built on it. Conversion rate, cost per conversion (CPA) and return (ROAS) are all calculated from conversions. Define the conversion badly and they are all wrong. And because campaigns like Performance Max learn from it, a bad definition doesn’t stay in the report; it decides who sees your ads.
A tag or pixel on the website records the action, for example a visit to the thank-you page after an order. The ad platform matches it to ad clicks or views within the conversion window and adds it to the stats. In Google Ads every conversion action is either primary or secondary:
| Action type | Google Ads column | Used for bidding |
|---|---|---|
| Primary | Conversions | Yes, if the goal it belongs to is used for bidding |
| Secondary | All conversions | No, observation only (custom goals are the exception) |
A purchase should carry the order value, ideally excluding VAT and shipping so it lines up with your return calculations. Purchases are counted as “Every”, because one person can order more than once. Leads are counted as “One”, so a page refresh or a second form from the same person doesn’t double the result.
| Conversion value | sum of primary conversion values | Example: 100 purchases × €50 average = €5,000 |
What happens when add-to-carts sit among your primary conversions? Move the sliders. The calculator assumes each cart carries the value of the goods, as it often does in tracking setups.
For an online store, only a completed purchase with the order value. For a service business, a submitted lead or a call. Add-to-carts, clicks on the phone number, newsletter sign-ups and other micro-conversions belong among secondary conversions: you see them in reports, bidding doesn’t learn from them. That is our rule.
At Papírnictví VojTech, campaigns counted add-to-cart as a purchase and a duplicate purchase tag was firing as well. In March 2026 only 8% of reported conversions were real purchases, and in April ads claimed 167% of the store’s actual revenue (case study). At Letsport, campaigns kept learning from zero-value contact clicks until August 2026, when we moved the “Contact” conversion to secondary (case study). At Elektro Sláma, rebuilding measurement so that only purchases count was part of the work after takeover (case study).
In Google Analytics 4, conversions have been called key events since 2024. Meta reports them as results from the pixel and the Conversions API. Each system credits them by different rules, so conversion counts never match exactly across platforms. Which source to trust is a question of attribution. The final word belongs to your store’s back office.
| Term | Formula / source | What it answers | When to use it |
|---|---|---|---|
| Conversion | count of primary actions | How many times success happened | The base of every performance metric |
| Conversion value | sum of order values | How much revenue ads report | Return targets in ecommerce |
| Conversion rate | conversions ÷ visits × 100 | How many visits end in success | Quality of site and traffic |
| CPA | spend ÷ conversions | What one success costs | Lead gen |
| Attribution | crediting rule | Which channel gets the conversion | Comparing channels |
Terms that stand or fall with what you count as a conversion.
There are many more carts than purchases, so the account suddenly looks highly profitable. Automated bidding then learns to find people who add to cart, not people who pay. At Papírnictví VojTech, carts made up 81% of “conversions”. Add-to-cart belongs among secondary conversions.
When a store also counts contact clicks as primary, return-target campaigns get a signal that earned nothing. Bids get spread between people who called about a return and people who bought. Track contacts, but don’t let bidding steer by them.
A duplicate tag on the thank-you page, or the same purchase set as primary both from the Google Ads tag and from a GA4 import. The result is the same: double the conversion value, half the CPA, and an ACoS that doesn’t match your P&L. The check is simple: compare purchases in Google Ads with orders in the back office for the same week.
An action you count as success for your ads or website: a purchase, a submitted lead, a phone call. In ad platforms it is a tracked event from which conversion rate, cost per conversion and return are calculated.
As a primary conversion, only a completed purchase with the order value, ideally excluding VAT and shipping. Set add-to-carts, contacts and sign-ups as secondary so automated bidding doesn’t learn from them.
In Google Ads, primary conversions appear in the Conversions column and automated bidding learns from them. Secondary conversions appear in All conversions and are for observation only, except within custom goals.
A conversion is a single action; conversion rate is the share of visits that ended in one. A hundred visits and two purchases mean two conversions and a 2% conversion rate.
Each system credits conversions with a different attribution model and window, GA4 may not see visitors who declined cookies, and Google Ads reports a conversion on the date of the click. A small gap is normal; a large one usually means a measurement error.
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