Science-related crowdfunding enables public engagement with science. However, we know little about citizens engaging with science this way: Who are the people engaging with and donating to science through crowdfunding - and how do they decide how much to give? This study analyses behavioural and survey data from the Swiss crowdfunding platform wemakeit (N = 576). Results illustrate that a small, non-representative segment of the public engages with science through crowdfunding. Compared to the general public in Switzerland, these backers have an above-average education and income. Science-related crowdfunding mainly reaches citizens with an existing interest in science, personal ties to project initiators or the scientific community. The size of backers' donations correlates with perceived personal appeals in campaigns or connections to initiators rather than projects' scientific merit. While science-related crowdfunding thus opens up new avenues for public outreach by the scientific community, its potential for broader public engagement with science seems limited.