Final answer:
The conversion rate is the primary metric to measure the effectiveness of a CTA in directing traffic to a landing page, indicating the success of the CTA's persuasion.
Step-by-step explanation:
The main gauge to determine the effectiveness of your Call To Action (CTA) at generating traffic to your landing page is commonly the conversion rate.
This metric measures the percentage of users who follow through on the CTA's direction, such as clicking a link and performing a specific action after reaching the landing page. A high conversion rate indicates that the CTA is effectively persuading users to move to the next step in the marketing funnel, thereby serving its purpose and contributing to the overall campaign's success.