There is a way to calculate how many watts you need for your space, but you would need to decide on how big your space is first. I suppose you could add up your watts and then you would know how big of a space you can go up to as well. I've seen what the recommended watts per square foot is change over the years, not really to sure what the common consensus is these days. I will just make something up and call it 50 watts to the square foot. Also it is square foot because you only have to calculate for the floor space being covered by light, or the light foot print I suppose. You don't need to calculate for the cubic foot of the grow box, that would be more so for ventilation or Co2. So lets say you go small and have a 2 foot x 2 foot space that is 3 feet tall and you want 50 watts to the square foot. Then you would multiply 2 x 2 = 4 and then multiply 4 x 50 watt's = 200 watts for the space. I might not have the formula correct and as I said before I don't know what the recommended wattage is. At one point I recall it was 35 watts but that was years ago. Whatever the recommended watts actually is and whatever you have to work with I think this should give you an idea of what you need. If it was 35 watts to the square foot then 2' x 2' = 4' square feet x 35 watts per square foot = needing, 140 watts for the space. I think that is right.