square feet == 6 x 2 = 12 square feet
cubic feet == 6 x 2 x 7 = 84 cubic feet
rough approximations however..
seedlings 500 lumens per sq ft
veg 2500 lumens per sq ft
flower 10,000 lumens per sq ft
in flower for your 6x2 area you will want about 120,000 lumens - you could get away with 600w...