A new method to measure the superfluid fraction of a supersolid has been developed using the Josephson effect. This effect, typically observed in superfluids and superconductors, is also expected to occur in supersolids due to their spatially modulated superfluid density. The study demonstrates that individual cells of a supersolid can sustain Josephson oscillations, and from the current-phase dynamics, the superfluid fraction can be directly derived. The superfluid fraction, which quantifies the reduction in superfluid stiffness due to spatial modulation, was previously not experimentally measured. The research focuses on a cold-atom dipolar supersolid, revealing a relatively large sub-unity superfluid fraction, which supports the study of phenomena like partially quantized vortices and supercurrents. The findings open new research directions, potentially unifying the description of all supersolid-like systems. The superfluid fraction is defined as the ratio of the kinetic energy in a modulated system to that in a homogeneous one. The study shows that the superfluid fraction can be measured using Josephson oscillations, providing a direct link between the superfluid fraction and the coupling energy of the junction. The results are consistent with numerical simulations and theoretical predictions, demonstrating the existence of self-sustained Josephson oscillations in a supersolid. The superfluid fraction was found to decrease with increasing density modulation depth, aligning with Leggett's predictions. The study highlights the unique properties of supersolids, showing that they can sustain complex dynamics with mixed classical and quantum characteristics. The findings have implications for understanding supersolidity in various systems, including superconductors and quantum gases.A new method to measure the superfluid fraction of a supersolid has been developed using the Josephson effect. This effect, typically observed in superfluids and superconductors, is also expected to occur in supersolids due to their spatially modulated superfluid density. The study demonstrates that individual cells of a supersolid can sustain Josephson oscillations, and from the current-phase dynamics, the superfluid fraction can be directly derived. The superfluid fraction, which quantifies the reduction in superfluid stiffness due to spatial modulation, was previously not experimentally measured. The research focuses on a cold-atom dipolar supersolid, revealing a relatively large sub-unity superfluid fraction, which supports the study of phenomena like partially quantized vortices and supercurrents. The findings open new research directions, potentially unifying the description of all supersolid-like systems. The superfluid fraction is defined as the ratio of the kinetic energy in a modulated system to that in a homogeneous one. The study shows that the superfluid fraction can be measured using Josephson oscillations, providing a direct link between the superfluid fraction and the coupling energy of the junction. The results are consistent with numerical simulations and theoretical predictions, demonstrating the existence of self-sustained Josephson oscillations in a supersolid. The superfluid fraction was found to decrease with increasing density modulation depth, aligning with Leggett's predictions. The study highlights the unique properties of supersolids, showing that they can sustain complex dynamics with mixed classical and quantum characteristics. The findings have implications for understanding supersolidity in various systems, including superconductors and quantum gases.