The paper investigates the dependence of specific magnetic losses Р уд. on magnetic induction amplitude B m in certified reference materials (CRMs) of electrotechnical steel properties. This dependence is shown to have power mode Р уд = a • (B m) b. Parameters a and b of this dependence for 30 units of certified reference materials of three approved CRM types were established. Measurement uncertainties Р уд due to the influence of B m on Р уд^ were evaluated.