Legal proportionality is one of the most important principles for adjudicating among conflicting values. However, rather little is known about the factors that play a role in the formation of proportionality judgments. This research presents the first empirical analysis in this regard, relying on a sample of 331 legal experts (lawyers and legal academics). The policy domain addressed by the experiment is the antiterrorist military practice of targeted killings, which has been the subject of a legal debate. Our experimental findings suggest that proportionality judgments are receptive to normatively relevant facts. We also find strong correlational evidence for the effect of ideological preferences on such judgments. These results are consistent for two proportionality doctrines. We suggest that proportionality judgment is anchored jointly in the experts’ policy preferences and the facts of the case. We outline the implications of the findings for the psychological and legal literature.