A method determines tolerance intervals for a set of dimensions of a part. The tolerance intervals are defined so that a part, the dimensions of which are included in the intervals, observes a set of constraints with a determined failure probability. The method includes generating a separation function for each constraint to be observed, each function being able to indicate whether a given dimensioning of a part meets or not the corresponding constraint. The method also includes iteratively building a set of increasingly larger tolerance intervals at each iteration, by the separation functions, whether the dimensionings included in the intervals observe the constraints with a failure probability of less than the failure probability.