The invention relates to a method and an apparatus for the direct determination of spatial dimensions of a light beam with high precision and short measuring period, which are also suitable for the measuring of laser beams with high power in the range of the beam focus. For this purpose, an apparatus is proposed that includes a beam scanner, at least one light sensor, a movement device for the execution of a relative movement between the light beam and the beam scanner, and a device for the signal recording of a temporally variable signal of the light sensor. The beam scanner comprises at least one scanning body with at least three sampling areas, which extends along sampling lines. The sampling areas are configured for the extraction of linear or strip-shaped light samples from a cross-section of the light beam. Several scanning surfaces are defined by the sampling lines of the sampling areas, each spanned by a movement vector of the relative movement. At least three scanning surfaces have a non-zero distance from one another in the direction of the axis of the light beam. The light sensor is configured for the detection of at least a portion of the sampled light extracted by the sampling areas from the cross-section of the light beam.