The average amount of eye contact adults make is 30-60% per conversation, 60-70% if they feel invested.
In many countries and regions of the world, take East Asia for instance, looking someone in the eye is considered rude. If that person is above you on the social hierarchy, say a professor, parent, or boss, doing so can be considered defiant. In the West however, maintaining eye contact is a sign of respect and earnestness. Avoiding eye contact is thought to be for a reason, such as you are lying, anxious, socially awkward, guilty, or untrustworthy. Sometimes it even telegraphs boredom with the topic of discussion.