 In the Senate ( the upper house ) , there are 76 senators : twelve each from the states and two each from the mainland territories ( the Australian Capital Territory and the Northern Territory ) . The House of Representatives ( the lower house ) has 150 members elected from single @-@ member electoral divisions , commonly known as " electorates " or " seats " , allocated to states on the basis of population , with each original state guaranteed a minimum of five seats . Elections for both chambers are normally held every three years simultaneously ; senators have overlapping six @-@ year terms except for those from the territories , whose terms are not fixed but are tied to the electoral cycle for the lower house ; thus only 40 of the 76 places in the Senate are put to each election unless the cycle is interrupted by a double dissolution . 
