Abstract: A brake cylinder of a motor vehicle, in particular a pneumatically actuatable brake cylinder of a commercial vehicle, includes a first housing part and a second housing part. An actuation tappet actuates a brake lever of a brake application device, which actuation tappet protrudes from a spring chamber of the first housing part. A membrane, which divides an interior bounded by the first housing part and the second housing part into a pressure chamber and the spring chamber, is provided, as well as a return spring for returning the actuation tappet from a braking position to a non-braking position. The return spring is arranged in a loaded manner between a housing bottom of the first housing part and a plate, which is arranged on the spring chamber side of the membrane and is connected to the actuation tappet. The return spring is provided with at least one elongation-measuring element.