Biomass mapping is used in variety of applications including carbon assessments, emission inventories, and wildland fire and fuel planning. Single values are often applied to individual pixels to represent biomass of classified vegetation, but each biomass estimate has associated uncertainty that is generally not acknowledged nor quantified. In this study, we developed a geospatial database of wildland fuel biomass values to characterize the inherent variability within and across major vegetation types of the United States and Canada. For vegetation types that had sufficient quantification of biomass by fuel type (e.g., canopy, shrub, herbaceous, fine downed wood, coarse downed wood, and organic soil layers), we developed empirical distribution estimates. Based on available data, fitted distributions will be useful for informing the first‐generation biomass mapping that incorporates variability in loading by vegetation and fuel type and to evaluate potential errors in point estimates given in current map products. Because combustible biomass is a common input in fire and smoke models, variability estimated for fitted distributions can be used to inform data input uncertainty in predictions of wildland fuel consumption and emissions and to provide stochastic inputs of biomass to ensemble simulation models.