A method to measure the brake force for railroad vehicles without replacing any part of the braking system, comprising the steps of opening a clearance between the braking elements, inserting a special sensor between the braking elements and applying the brake followed by the processing of the signal generated by the sensor and displaying the result in force units. A device to measure the brake force for railroad vehicles, which uses a sensor, the main part of which is a prismatic steel plate (3) with strain gauges (4a, 4b, 5a, 5b,) on both sides. To measure the brake force, the sensor is positioned, depending on the braking system, between the brake shoe (1) and the wheel tread (2) or between the brake pad and the brake disc. When the brake is applied, the sensor comes in contact with the braking surfaces (brake shoe / brake pad and wheel tread / brake disc) through (the intermediary of) four drill rods (6a, 6b, 7a, 7b,) affixed to the sensor body (3), two on each side, in such a way that the mechanical contact between each rod and the sensor body is over a line and the sensor is submitted to a bending moment. To make the device adaptable to any wheel diameter or wear of the brake components and to protect the brake shoe surface, each of the two rods (7a, 7b,) on the brake shoe side (for braking systems using a brake shoe), has a steel wing (8a, 8b,) elastically seated on it. The wings are kept in place by three rubber membranes (9, 11a, 11b,) connecting the wings between them and to the sensor body. The sensor is kept in place during measurements by two sets of magnets (13a, 13b) embedded into two rubber strips (12a, 12b,) bonded on two opposite sides of the sensor body (3).