Green building certification is a good start for the construction industry to benchmark the environmental impact of buildings. However, the green building certifications around the world disregard the carbon footprint calculation for certified buildings. The positive contribution of green building designs may not be reflected on the points and rating in the certification. It is hard to understand the environmental impact only through points. The New Building Institute (NBI) challenged the rating system because high credential buildings were not necessarily more green than low buildings. The incident raised questions about the real energy savings of green buildings. To address these concerns, a common benchmark should replace the current green building certification rating systems around the world. Since carbon emissions are widely used to measure the environmental impact of raw materials or fuels, such as gasoline, methanol, aggregates, and cement, they can also be applied in green building construction and operation. The paper: (1) determines the environmental impact in green building certification criteria; (2) finds relationship between green building ratings and carbon emissions; (3) establishes a carbon emission calculation system for green buildings certification. The results show that the green features, such as the use of greenery, and water saving fittings, used in green buildings lower water and energy consumption, and they lower the environmental impacts to the environment.