Transformer Core Area
The reason behind using laminated cores is minimising eddy currents and therefore heat losses. If solid iron core was used, the current could be induced and flow in three degrees of freedom.

However, because the core consists of laminated sheets, such as E-I, M or C sheets, current cannot create a loop because the circumference around the coils is always split into two or more elements (no current can flow between E and I). And because sheets in the sheet stack are insulated from each other, no current can flow 'sideways'.

Still, some current is induced along the elements. To minimize this, high resistivity steel is used.

The area of laminated core is higher because of the added thickness of insulation (oxide/laquer) between individual layers of iron.