AbstractThe tendency of trees to grow taller with increasing water availability is common knowledge. Yet a robust, universal relationship between the spatial distribution of water availability and forest canopy height (H) is lacking. Here, we created a global water availability map by calculating an annual budget as the difference between precipitation (P) and potential evapotranspiration (PET) at a 1‐km spatial resolution, and in turn correlated it with a global H map of the same resolution. Across forested areas over the globe, Hmeanincreased with P‐PET, roughly: Hmean(m) = 19.3 + 0.077*(P‐PET). Maximum forest canopy height also increased gradually from ~ 5 to ~ 50 m, saturating at ~ 45 m for P‐PET> 500 mm. Forests were far from their maximum height potential in cold, boreal regions and in disturbed areas. The strong association between forest height and P‐PETprovides a useful tool when studying future forest dynamics under climate change, and in quantifying anthropogenic forest disturbance.