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How can i measure the area of the coils in my home made generator?

How can i measure the area of the coils in my home made generator?and in that generator i have 15 coils and each coil have 40 turns so when i am calculating the e.m.f of generator E=BAnW in this equation i have to put the no of turns of all the coils or just the no.of turns of each coil?