4x4, and how many you can fit depends on amount of veg time,4 weeks veg should just about fit 9 plants,but you also have to factor in pot size too.
do you wanna veg for a long time or for a short time?so it can be 1 big plant,or loads of small ones.
but in the past i have grown 9 in that space after a 5 week veg.they were all topped,they were in 11 litre pots in 3 rows of 3.they took up every inch of space,but it looked great seeing the canopy of colas.