1) Airiness 2) Commodiousness 3) Roominess 4) Spaciousness 1) Bigness 2) Commodiousness 3) Largeness 4) Roominess 5) Spaciousness 6) Spatial largeness 
• (n.) The quality of being capacious, as of a vessel, a reservoir a bay, the mind, etc.
Ca·pa'cious·ness noun The quality of being capacious, as of a vessel, a reservoir a bay, the mind, etc. 
[n] - spatial largeness (especially inside a building)
roominess noun spatial largeness and extensiveness (especially inside a building); `the capaciousness of Santa`s bag astounded the child`; `roominess in this size car is always a compromise`; `his new office lacked the spaciousness that he had become a...