Sorry for the inconvenience. Please download the latest version of the data from version 02 using this link:: https://doi.org/10.5281/zenodo.10118907. Forests are a major terrestrial carbon sink, but anthropogenic changes in land use and climate have considerably reduced the scale of this system1. Remote-sensing estimates to quantify carbon losses from global forests2–5 are characterized by considerable uncertainty, and we lack a comprehensive ground-sourced evaluation to benchmark these estimates. Here, we combine multiple ground-sourced6 and satellite-derived approaches2,7,8 to evaluate the scale of the global forest carbon potential outside of agricultural and urban lands. Despite regional variation, the predictions demonstrated remarkable consistency at a global scale, with only 12% difference between the ground-sourced and satellite-derived estimates. Currently, global forest carbon storage is significantly below the natural potential, with a total deficit of 226 Gt (model range = 151-363 Gt) in areas with low human footprint. Most (61%, 139 Gt C) of this potential is in areas with existing forests, where ecosystem protection can allow forests to recover to maturity. The remaining 39% (87 Gt C) of potential lies in regions where forests have been removed or fragmented. Although forests cannot be a substitute for emissions reductions, our results support the idea2,3,9 that the conservation, restoration, and sustainable management of diverse forests offer valuable contributions to meeting global climate and biodiversity targets.