Based on the cross-national survey part of the so called Peoples' Internet (PIN) Project, the article1 analyzes social media uses in three different world regions: Europe, US, and China. Within the tradition of the studies on the social uses of the media, the article describes different kinds of social media uses, focusing on different factors that contribute to shape them in a more or less private or public way. Social media practices do not differentiate in a simply dichotomous way, as "private" or "public"; rather, they are gradually articulated in a "scalable sociality" that integrates, in different ways, elements of privateness and publicness. In the definition of such a scale, structural and cultural differences among different world regions and single countries play a role, alongside with variables as socio-demographic features, available capitals, and civic attitudes. [ABSTRACT FROM AUTHOR]