This paper projects the average household size in China, and decomposes the total residential consumption into the factors of population size, household size, and consumption levels. The study finds that the average household size fluctuates around 2.5 persons per household. The proportion of households with 1 person and 2 persons will rise, 3-person and 4-person households will account for the largest proportion, while the proportion of 5-7-person households will decrease. The growth of 1-person and 2-person households is the major driving force of the growth of residential consumption. The influence of changes in household size on residential consumption exceeds that of consumption level. The changes in demographic and household factors have its own inertia, which has a rigid effect on the consumption growth. Under the trend scenario, the contribution of demographic factors to consumption will decrease while that of household factors will increase. Because changes in household size have a profound impact on society, economy, and the environment, policymaking should take into account the potential impact of changes in household size.