Green building development in China relies mainly on compulsory measures that lack incentive policies to motivate the enthusiasm of real estate developers. A floor area ratio bonus is encouraged by the Chinese State Council. In order to ensure the feasibility of a reward quota, residential buildings that met the requirement for energy efficiency during the official assessment in Ningbo in 2014 were selected as research objects. The amount of energy and water savings in terms of the Assessment Standard for Green Building is converted into carbon emissions. Carbon emissions of different star-rated green buildings are then measured in accordance with the actual water and power consumption of residential dwellings in 2014. A regression equation is set up concerning the floor area ratio and index for residential land per capita. A carbon emission-based method is proposed for measuring the reward quota associated with floor area ratio and recommendations are given for development using green building.