Abstract: A variable size air mattress that has at least a first plenum, a second plenum side-by side with said first plenum, a first inflation/deflation valve for the air mattress communicating with said first plenum, and a second inflation/deflation valve communicating with said second plenum, to allow inflation for only the first plenum when said first inflation/deflation valve is open but said second inflation/deflation valve is closed, or when both said first and second inflation/deflation valves are open, communicating with said first plenum and said second plenum so that when inflated the air mattress is a larger size of a double bed mattress, a queen bed mattress, or a king bed mattress, depending on the size of said first and second plenums. The air mattress may further include a third plenum, such that said second and third plenums are on either side of said first plenum.