Here goes, hope the sums are ok. Display is 4x2x2 which makes it same as yours 72, sump (this is in mm) 500x600x1000 which is about 44Gallons, total being 116.
Actually, 4' x 2' x 2' = 120g, not 72g. That's a pretty big difference. Give your tank the credit it deserves -- don't short it those 48g! You don't want to hurt it's ego...
