Pore-scale observation of vortical flow structures in porous media is a significant challenge in many natural and industrial systems. Vortical structure dynamics is believed to be the driving mechanism in the transition regime in porous media based on the pore Reynolds number, Re p . To examine this assertion, a refractiveindex matched randomly packed porous medium with homogeneously-sized glass spheres (D B = 15mm) is designed to measure the scale of vortical flow structures in transition from unsteady laminar to turbulent using two-dimensional time-resolved particle image velocimetry. Planar Particle Image Velocimetry (PIV) data is used to quantify the scale of these structures with regard to size, strength, and number density using two different scalings (i) Re p macroscopic (global), and (ii) Re p microscopic (local, pore-scale). Data is obtained for Re p from 100 to 948 in six different locations from the center of the bed towards the wall (one bead diameter away from wall). Direct measurement of vortex scale is quantified by employing swirl strength (λ ci ), vortex core (Γ 2 ), and enhanced swirl strength (λ cr /λ ci ) vortex identification methods. These scales are compared with turbulent integral scales. Due to the confinement of the random medium, the inertia-dependent topology of the flow creates shear-dominant vortical structures in moderate unsteady laminar Reynolds numbers (Re p < 300), while the swirl-dominant flow structures appear in weak turbulent Reynolds numbers (Re p > 500). From the macroscopic point of view, (i) the size of vortical structures decreases asymptotically to reach 20% of the global hydraulic diameter, (ii) the strength of vortices increases monotonically by enhancing the inertial effects of Re p , and (iii) the average number density of vortical structures grows from unsteady laminar to fully turbulent. From the pore-scale (local) point of view using Re p , (i) the size of vortical structures decreases monotonically with increasing local Reynolds number, (ii) the strength of vortices rises with Re p , and (iii) the number density of vortical structures for different Re p is invariant relative to the pore size. These findings suggest pore versus macro-scale coupling exists for the scale of vortical flow structures in the transition regime, albeit the scale variation of pore-scale flow structures with local inertial effects is different from the asymptotic values captured in the macroscopic level with increasing Re p .