Engagement Rate on Facebook - numbers

Hi,

our company is using different metrics to analyze the ongoing campaigns on Datastudio.

One of the metrics is the engagement rate.

I wanted to ask which of the KPIs are used to calculate this metric.

In the metric list for Facebook Insights the Engagement Rate is listed as "% of reached people who clicked". I would need the numbers that are put in relation in order to explain it also to other colleagues.

Thank you in advance