Candid Charm - Cauliflower

As i got my cauliflower seeds from seed parade I have no instructions!  I have read that I can harvest them from tennis ball size so I can plant them 'relatively' close together, what is 'relatively in cm or inches???'  I will leave some to fully mature but as I am the only one that eats them and I have about 10 at different stages  I dont have the room for 2' apart. (I couldnt thin out the weakest seedling they looked the same nice and strong ... so I potted them all on!)