depends. at 25 square feet if most your area is covered with plants a 1000 watt would be perfect for your flowering space. That would be optimal at 40 watts per square foot. you can get away with less. Basically you want at least 30 watts per square foot with 40-50 being optimal for flowering. For Veg I would say around the same but you could cut it back a tad. If I had your space I would be running a 600 MH in my veg room and a 1000 watt hps in my flower room. If your looking for minimal values I would say 30 watts per square foot is the lowest you should go for quality plants IMHO.