example: say 800 heads per week. and it takes 8 weeks from seedling to harvest for the lettuce you want to grow.
multiply 800 x 8 = 6400 you would need a 6400 unit system greenhouse. you would start by putting 800 plants a week until the system is completely full and on at the end of the 12 week you harvest the first 800 heads and replace that 800 with 800 new seedlings every week. That is known as the Sea of Green method of growing on a large scale.