A 6x6 isn't two times bigger than a 3x3, it's four times bigger. 3x3=9, 6x6=36. I've been equating a meter to 3', but it's really 3.28', so for the below info I'm going to use that value.
I only know the led wattage rule of thumb for square feet, but If 1 square foot = 0.092 square meters and...