We provide a framework to decompose preferences into a notion of distributive justice and a selfishness part and to recover individual notions of distributive justice from data collected in appropriately designed experiments. "Dictator games" with varying transfer rates used in Andreoni and Miller (2002) and Fisman et al. (2007) can be used to assess individuals' preferences, but - with the help of simple new axioms - also to recover some part of individuals' notion of justice. "Social planner" experiments or experiments under a "veil of ignorance" (Rawls 1971) can be used to recover larger parts of the notion of justice. The axioms also allow a simple test for the validity of such an experimental approach, which is not necessarily incentive-compatible, and to recover a greater part of an individual's preference relation in dictator experiments than before. Interpersonal comparison of the individual intensity of justice (or fairness) similar to the suggestions in Karni and Safra (2002b) are possible, and we can evaluate the intensity based on an individual's own notion of justice. The approach is kept completely non-parametric. As such, this article is in the spirit of Varian (1982) and Karni and Safra (2002a).