Abstract Chemical erosion governs the evolution of fractures across Earth systems, which manifests in three distinct dissolution patterns. However, how the boundaries between these regimes depend on system scale remains an open question, and no predictive theory has successfully linked laboratory observations to field‐scale behaviors. Here we integrate experiments, simulations, and linear stability analysis to show that fracture‐dissolution patterns across almost three orders of magnitude in length collapse onto a universal phase diagram defined by two dimensionless parameters, one of which explicitly incorporates fracture length. We derive analytical thresholds for transitions between compact, wormholing, and uniform dissolution and validate them against data with fracture length ranging from 0.1 to 30 m. We demonstrate that the optimal injection rate for maximizing permeability enhancement scales linearly with fracture length, enabling direct extrapolation from core‐flood experiments to field conditions. These findings provide a quantitative basis for upscaling dissolution dynamics in fractured geologic media.