function calculateGAMetrics() {
var traffic = parseFloat(document.getElementById('ga_traffic').value);
var conversions = parseFloat(document.getElementById('ga_conversions').value);
var cost = parseFloat(document.getElementById('ga_cost').value);
var resultBox = document.getElementById('ga_results');
// Validation: Traffic must be a positive number
if (isNaN(traffic) || traffic <= 0) {
alert("Please enter a valid number for Total Traffic (Sessions/Users).");
return;
}
// Validation: Conversions must be a number
if (isNaN(conversions) || conversions 0) {
frequency = traffic / conversions;
}
// 3. Calculate CPA (if cost is provided)
var cpa = 0;
var showCPA = false;
if (!isNaN(cost) && cost > 0 && conversions > 0) {
cpa = cost / conversions;
showCPA = true;
}
// Display Results
document.getElementById('res_cr').innerHTML = conversionRate.toFixed(2) + "%";
if (conversions > 0) {
document.getElementById('res_freq').innerHTML = "1 in every " + Math.round(frequency) + " visits";
} else {
document.getElementById('res_freq').innerHTML = "No conversions";
}
if (showCPA) {
document.getElementById('row_cpa').style.display = 'flex';
document.getElementById('res_cpa').innerHTML = "$" + cpa.toFixed(2);
} else {
document.getElementById('row_cpa').style.display = 'none';
}
resultBox.style.display = 'block';
}
How is Conversion Rate Calculated in Google Analytics?
Understanding the math behind your analytics dashboard is crucial for accurate data interpretation. While Google Analytics automates this process, knowing the specific formula helps you audit your data and set realistic targets. The calculator above simulates the logic used by both Universal Analytics (UA) and Google Analytics 4 (GA4).
The Core Formula
At its most basic level, the conversion rate in Google Analytics represents the percentage of traffic that completes a specific goal (such as a purchase, form fill, or newsletter signup). The mathematical formula is:
For example, if your website receives 1,000 sessions and generates 50 sales, the calculation is:
(50 ÷ 1,000) = 0.05
0.05 × 100 = 5% Conversion Rate
Session Conversion Rate vs. User Conversion Rate
It is critical to note that "Traffic" can be defined in two ways, resulting in two different metrics within Google Analytics:
Session Conversion Rate: This is the standard metric in Universal Analytics. It calculates the percentage of sessions that resulted in a conversion. One user can have multiple sessions.
User Conversion Rate: This is more prominent in GA4. It calculates the percentage of unique users who converted. This number is typically higher than the session conversion rate because one user usually visits multiple times before converting.
Why Do the Numbers Differ Between UA and GA4?
If you are migrating from Universal Analytics to GA4, you might notice a discrepancy in your conversion rates. This is primarily due to how "Conversions" are counted:
Universal Analytics: Counts only one goal completion per session for a specific goal ID. If a user submits the same form twice in one session, it counts as 1 conversion.
Google Analytics 4: Historically counted every event as a conversion. While settings now allow you to count "once per session," the default event-based model can lead to higher conversion counts if users trigger the conversion event multiple times (e.g., reloading a thank-you page).
How Cost Per Acquisition (CPA) Relates
While not a direct conversion rate metric, CPA is inextricably linked. As shown in the calculator above, if you input your ad spend, you can determine how much you are paying for each conversion. The formula used is:
Total Cost ÷ Total Conversions = CPA
High conversion rates are desirable, but only if the CPA remains profitable relative to your customer lifetime value.