11.8" in length, 15.7" in width and 71.4" in height.. You could fit two 2 gallon airpots in there if you lined them up diagonally i.e: one in top left corner, other one touching the other and in the bottom right corner.
Hopefully you're not doing stealth. Then you can mount equipment on the outside (i.e: fan, carbon filter) and use a light like LED or CFL you can maximize the space. Any sort of HID lighting in a set-up that small would run rather hot. What were your plans/thoughts about the space?