A magnetizer design methodology that takes into account systematic errors such as the variation in flux density (B), and the z-component of the magnetic field (H-z), is proposed. The effect of the sample diameter and the effective length of the yoke, i.e. yoke depth on H-z are analysed. Experimental results at 1.5 T and 60 H-z showed a reduction of 81 %, 72 % and 30 % by a large magnetizer, shielding and reducing the yoke depth from 80 mm to 10 mm, respectively. This was in comparison to an unshielded compact magnetizer. H-z is also dependent on magnetic loading. Furthermore, at 2 T and 60 Hz, magnetic contributions dominated H-z such that the effectiveness of shielding and reducing the yoke depth decreased to 27 % and 4 %, respectively. To achieve these very high flux densities, the magnetizers were designed to be compact (sample diameter of <= 100 mm and narrow airgaps of <= 2 mm). This reduction in size increases the leakage field above and below the sample to the same level of magnitude as the applied field, which affects the measurement of the magnetic field (H). Two H-coil sizes with a sensitivity difference of 60 % are used to show that the measured H is independent of the coil size, but depends on the leakage field. Their measured core loss difference under pulsating and rotating fields was about 6 %.