The increasing occurrence of natural hazards such as wildfires and drought, along with urban expansion and land consumption, causes increasing levels of fire risk to populations and human settlements. Moreover, increasing geopolitical instability in many regions of the world requires evaluation of scenarios related to potential hazards caused by military operations. Quantitative knowledge of burnable fuels and their spatiotemporal distribution across landscapes is crucial for risk and potential damage assessments. While there is a good understanding of the distributions of biomass fuels based on remote sensing observations, the combustible mass of the built environment has rarely been quantified in a spatially explicit and detailed manner. Therefore, we developed fine-grained estimates of urban fuels for the conterminous United States, estimating the combustible mass of building materials, building contents, and personal vehicles at 250 m spatial resolution. The resulting dataset is called COMBUST (COmbustible Mass of the Built environment in the conterminous United STates) and is currently the most comprehensive dataset of combustible mass and materials for the U.S., covering over 110 million structures. COMBUST includes different backcasting scenarios from 1975 to 2020 and is based on the integration of a variety of geospatial data sources such as Earth-observation derived data, real estate data, statistical estimates and volunteered geographic information. COMBUST is accompanied by COMBUST Plus, a set of consistently enumerated gridded datasets facilitating combustion exposure modelling of buildings and population. These datasets constitute a rich resource for ecological and social science applications, as well as for disaster risk management, planning and decision making. COMBUST is available at <a href="https://doi.org/10.5281/zenodo.15611963">https://doi.org/10.5281/zenodo.15611963</a>.