Most people in Europe live in urban environments. For these people, urban green space is an important element of well-being, but it is often in short supply. We use self-reported information on life satisfaction and two individual green space measures to explore how urban green space affects the well-being of the residents of Berlin, the capital city of Germany. We combine spatially explicit survey data with spatially highly disaggregated GIS data on urban green space. We observe a significant, inverted U-shaped effect of the amount of and distance to urban green space on life satisfaction. According to our results, the amount of green space in a 1 km buffer that leads to the largest positive effect on life satisfaction is 35 ha or 11% of the buffer area. In our sample, 75% of the respondents have less green space available.