<p>Liquefaction of saturated soils is typically characterized by macroscopic variables such as pore pressure ratio and double-amplitude strain, which often fail to capture the underlying microscopic mechanisms and may lead to inconsistent judgments under certain conditions. To overcome these limitations, this study utilizes the inertial number — a concept originally proposed for granular materials — to characterize the soil liquefaction process. Through integrated experimental tests on multiple soil types (Nanjing fine sand, silt, calcareous sand) and discrete element method (DEM) simulations, the micro-macro physical significance of the inertial number is revealed as the ratio of the microscopic particle rearrangement time scale to the macroscopic shear deformation time scale. The evolution of the inertial number follows a Boltzmann distribution curve, effectively capturing the three-stage characteristics of liquefaction: initial stability, rapid transition, and post-liquefaction stabilization. Results demonstrate that the inertial number synchronously integrates the evolution of pore pressure and strain, providing a unified criterion for liquefaction identification. Moreover, it shows great potential for predicting post-liquefaction behavior and serving as a governing parameter in liquefaction analysis. Future work will focus on validating its applicability through centrifuge tests and integrating field data (e.g., CPT/SPT) for engineering-scale applications.</p>