This study investigates the relationship between social network site (SNS) activity and social well-being, focusing on social capital and loneliness. The research validates a self-report scale using Facebook activity data, tests the generalizability of previous findings to older and international populations, and explores the specific activities linked to social capital and loneliness. Directed communication, such as wall posts, comments, and "likes," is associated with greater bonding social capital and lower loneliness, but has only a modest relationship with bridging social capital, which is related to network size. Conversely, users who consume more content report reduced bridging and bonding social capital and increased loneliness. The study also finds that overall SNS activity, particularly friend count, is positively correlated with both types of social capital and negatively correlated with loneliness. However, time spent on the site is highly correlated with friend count and content production, but not a significant predictor of well-being after controlling for friend count. The Facebook Intensity Scale, which measures self-reported activity, correlates moderately with actual site behavior. Directed communication plays an expected role in bonding social capital, while consumption is associated with reduced bridging social capital and increased loneliness. The study suggests that the Facebook Intensity Scale is a reasonable measure of SNS use, though server data may provide more accurate insights. The findings indicate that SNS use is associated with increased social capital and reduced loneliness, but the relationship between consumption and loneliness is complex. The study also highlights the importance of considering the quality of content in the feed, as low-quality content may reduce users' sense of connection. The results suggest that SNS use is correlated with greater overall well-being, and that design enhancements could focus on fostering communication over passive engagement. The study acknowledges limitations, including the inability to assess causality and the potential influence of cultural norms on results. Future research will explore the causal relationship between SNS use and social well-being.This study investigates the relationship between social network site (SNS) activity and social well-being, focusing on social capital and loneliness. The research validates a self-report scale using Facebook activity data, tests the generalizability of previous findings to older and international populations, and explores the specific activities linked to social capital and loneliness. Directed communication, such as wall posts, comments, and "likes," is associated with greater bonding social capital and lower loneliness, but has only a modest relationship with bridging social capital, which is related to network size. Conversely, users who consume more content report reduced bridging and bonding social capital and increased loneliness. The study also finds that overall SNS activity, particularly friend count, is positively correlated with both types of social capital and negatively correlated with loneliness. However, time spent on the site is highly correlated with friend count and content production, but not a significant predictor of well-being after controlling for friend count. The Facebook Intensity Scale, which measures self-reported activity, correlates moderately with actual site behavior. Directed communication plays an expected role in bonding social capital, while consumption is associated with reduced bridging social capital and increased loneliness. The study suggests that the Facebook Intensity Scale is a reasonable measure of SNS use, though server data may provide more accurate insights. The findings indicate that SNS use is associated with increased social capital and reduced loneliness, but the relationship between consumption and loneliness is complex. The study also highlights the importance of considering the quality of content in the feed, as low-quality content may reduce users' sense of connection. The results suggest that SNS use is correlated with greater overall well-being, and that design enhancements could focus on fostering communication over passive engagement. The study acknowledges limitations, including the inability to assess causality and the potential influence of cultural norms on results. Future research will explore the causal relationship between SNS use and social well-being.