If the area of I-H hysteresis loop and B-H hysteresis loop are denoted by A1 and A2 respectively, then

In SI unitsB=μ0(H+I) or dB=μ0dH+μ0dI ∴∮  H⋅dB=μ0∮  H⋅dH+μ0∮  H⋅dI  or ∮  H⋅dB=μ0∮  H⋅dI (∵∮  H⋅dH=0)or area of B-H loop = μ0 (area of I-H loop).