Magnetic field sensors are used intensively in many areas of our lives and the demands on their properties are constantly growing. One of the biggest challenges is the development of an offset-free sensor that provides a zero signal at zero field, regardless of the manufacturing accuracy. Here, we propose the concept of an offset-free sensor, based on the use of standing spin waves. The dispersion of the spin waves strongly depends on the applied magnetic field, so that the excitation maximum of the standing wave shifts with the change of the field. Spin pumping in combination with the inverse spin Hall effect is used to detect the sensor signal directly, in the form of a dc voltage. The offset-free functionality is achieved by reversing the magnetization direction of the spin-wave waveguide. The functionality of the sensors is proven numerically and concepts for practical implementation are presented.