This tool is a computer application that reads publicly available forest inventory data collected by the USDA Forest Service, Forest Inventory and Analysis Program (FIA) and develops annualized estimates of forest carbon stocks.  Estimates can be recalculated as new inventory data become available.  Outputs are spreadsheets of annualized forest carbon stock and stock changes beginning in 1990 through the present for the conterminous United States.  These results can be also classified according to State or ecosystem carbon pool.  Inventory to carbon conversions are based on established inventory based factors and the stock change method, which requires consistent sequential sets of inventory data.  We provide an overview of methods to adapt and augment FIA data to produce the carbon estimates.  The carbon calculation tool replicates the process the USDA Forest Service uses to generate forest carbon estimates supplied to the U.S. Environmental Protection Agency for the annual inventory of U.S. greenhouse gas emissions and sinks.