how big of a grow space with 400w?

I am wondering what sizze of a grow area does a 400w hps give you? thanks.

3x3 is a good foot print. I go more 4x4 but the out side is week.

If you have the funds, you could always purchase a 6 foot light mover. Ive used a light mover on a 430 and it kinda did the trick. But dont expect Huge buds. Good luck