A brake booster for a vehicle brake system includes a brake force transmitting element, a booster force transmitting element, a first rotation sensor, and a second rotation sensor. The brake force transmitting element is moveable in an axial direction for transmitting a pedal brake force from a brake pedal to a primary brake cylinder. The booster force transmitting element is moveable in the axial direction for transmitting a booster brake force to the primary brake cylinder. The first rotation sensor is kinematically coupled with the brake force transmitting element via a motion converting mechanism for measuring the axial position of the brake force transmitting element. The second rotation sensor is kinematically coupled with the booster force transmitting element for measuring the axial position of the booster force transmitting element. The measurements of the first and second rotation sensors are used for controlling the generation of the booster brake force.