You don’t want to stand too far away and come off as disinterested, but you also don’t want to be a space invader and make people uncomfortable, so what’s the expected amount of space?
In the United States, if you’re speaking to someone one-on-one, the amount of space has traditionally been thought of as 18 inches. But in an article by Amanda Erickson in the Washington Post about new cross-cultural research, you can see that it depends on how well you know the person and there is variability between countries and the closeness of the relationship.
The average man has an arm length of about 26 inches, which is about halfway between 18 inches customary for close relationships and 36 inches for acquaintances or strangers. So arm’s length is a good approximation of how much space to maintain.
Sorokowska, A., Sorokowski, P., Hilpert, P., Cantarero, K., Frackowiak, T., Ahmadi, K., … & Blumen, S. (2017). Preferred Interpersonal Distances: A Global Comparison. Journal of Cross-Cultural Psychology, 48(4), 577-592.