Objectives The main objective of this study was to describe the variation of individual social capital according to socio-demographic factors, and to develop a suitable way to measure social capital for this purpose. The similarity of socio-demographic variation between the genders was also assessed. Data and methods The study applied cross-sectional data from the national Finnish Health 2000 survey (n = 8,028) which represents the adult population, aged 30 years and over. Several variables indicating social capital were condensed to dimensions on the basis of factor analysis. Participants were categorized into tertiles in each dimension of social capital by means of factor scores. The multinomial logistic regression model was used to produce the adjusted prevalences for the dimensions of social capital according to socio-demographic categories (age, gender, education, living arrangements, income, and type of region). Results Three dimensions of social capital were distinguished: social support, social participation and networks, and trust and reciprocity. Age had an inverse association with social support as well as participation and networks, and a curvilinear association between age and trust and reciprocity, the oldest age groups showing the highest level of trust. Married persons and those in the highest educational and income groups tended to have more social capital than other persons. Residents of urban and rural regions did not systematically differ from each other in their level of social capital although residents of urban regions participated less and showed less trust than people living in semi-urban or rural regions. Social support varied significantly with gender. The decline of social support by age was steeper in women than in men. Social participation and networks increased with education, the gradient appearing steeper among men. The difference between married and cohabiting men was substantial compared to women when it came to trust. Conclusions People who are young, married, educated, and well-off have plenty of social capital. This information might help various services to concentrate the actions on the people in danger of social exclusion. Our results also form a basis for the future by allowing the changes in social capital to be examined over time and over different studies.