Summary: Seattle architecture firm Mithun has developed a free online building carbon calculator tool that quickly lets architects estimate the amount of carbon the construction of a building will release. Unlike most carbon calculators that focus on how much carbon a building will put into the atmosphere over its entire lifespan, Mithun’s tool (created with the help of the Lady Bird Johnson Wildflower Center at the University of Texas) estimates the embodied carbon emissions of a project.

Embodied carbon is the carbon released when a product is manufactured, shipped to a project site, and installed. Carbon released during project construction is a primary source of emissions, even when considered against the life of an entire building. Thirteen to 18 percent of the total embodied carbon footprint of any construction project is released the year the project is built. The Build Carbon Neutral calculator asks users to input above and below ground square footages, the primary structural system, and site conditions like eco-region and vegetation types that will be displaced. The resulting estimates are said to be accurate within 25 percent. The calculator is best used to approximate construction carbon emissions in the early stages of a design project and then refine its emissions from there. The online tool also includes information on offsetting carbon emissions.