I have six plants in my 2.5 x 2.5. If you are a rank beginner, I would expect you to grow about 1 oz. per plant. After a number of grows that could be three times as much. For a 4x4 tent I would look at a 400-450 watt light measured by current draw from your outlet. DO NOT buy cheap light. If you have not read GrowWeedEasy.com, I recommend doing so before you purchase anything, If you have already read it, I suggest rereading it.