What are the best metrics for measuring user engagement?

User engagement is a critical metric to understand for every business with an online component,

Measuring engagement breadth, how often a user visits your site.

(Number of visit by each user per day/week/month)

This is a key metric employed by the social network Facebook, amongst others.

To calculate it, calculate for each user how many days they’ve visited your website for each month:

Measuring engagement depth,

(Number of events per visit)

When looking at consumer Internet products, I split the metrics into two level whereas L1 = early stage, and L2 = traction for building real revenues at later stage...Level1:    Unique users per month    Pageviews per user per month    Minutes per user per monthLevel2:    Daily active users    Revenue per user per year    Comments per user    Retention and churn (if product has premium services)

Thank you for the kind invitation

I agree with Mr. Mounir answered adequately answered