Forest ecosystems are the largest terrestrial carbon sink on Earth, with more than half of their net primary production moving to the soil via the decomposition of litter biomass. The Forest Inventory and Analysis program within the Forest Service has been consistently measuring litter and soil attributes on permanent sample plots across all forest land and ownerships as part of the national forest inventory since 2001. Those data recently have been harmonized with auxiliary soils, climate, and geospatial data to develop models for predicting litter and soil carbon stocks on forest land in the United States for United Nations Framework Convention on Climate Change (UNFCCC) reporting. This work resulted in an estimated 44 percent reduction in litter carbon stocks and an estimated 40 percent increase in soil carbon stocks relative to previous estimates in UNFCCC reporting. More broadly, this work suggests that Intergovernmental Panel on Climate Change defaults and country-specific models used to estimate litter and soil carbon in temperate forest ecosystems may not well represent the contribution of these pools in national carbon budgets.