Hi Shake,
My grow area is ~ 28" x 18" (w x d) which is 2 1/3 foot by 1 1/2 foot. in total this makes ~ 3 1/2 square foot (2.33 multiplied by 1.5)

I aimed for 7500+ lumens per square foot so went for a 250watt HPS with 28000 lumens. So I get around 8000 per square foot (28000 divided by 3.5).

Yours would be 3.75 foot x 1.75 foot, so ~ 6.5 square foot.
6.5 sq ft x 7500 lumens = 48750 lumens total.

So a 400w HPS should be good as they put out around 50000 lumens. :thumbsup: