Transport of passengers is carried out essentially using two types of vehicles: classic trains composed of a locomotive pulling passenger wagons or traction units (or multiple units). Both new and modernized rail vehicles must be subjected to, among others, brake system tests when being placed into service. The purpose of such tests is to check the correct operation of the brake system and to determine the actual brake performance. The method of determining the passenger wagon brake performance differs from the similar method for the train set, although the braking performance of both types of vehicles is eventually presented in the form of two parameters: the value of brake mass B expressed in tons and the percentage of braked mass λ, i.e. the ratio of braked mass to vehicle total mass, expressed as a percentage. The values of B and λ determined from the tests describing the brake performance serve to assess the brake performance of the train in operation, while railway traffic safety relies significantly on the correct understanding of their nature and their use. Unfortunately, it was observed that individual carriers interpret these values in different ways and describe them in various ways on vehicles that are ultimately operated on the same infrastructure. The article presents a proposal of a new, original, unified and transparent method of describing brake performance for electric multiple units, as well as its interpretation and application in railway operations, developed in the Brakes Workshop of the Railway Institute.