Zinc oxide (ZnO) nanoparticles were synthesized using the coprecipitation method at 450°C. X-ray diffraction (XRD) confirmed the formation of a wurtzite phase, and transmission electron microscopy (TEM) revealed spherical particles with an average grain size of about 50 nm. The crystalline size and lattice strain were evaluated using the Williamson-Hall (W-H) analysis, along with other physical parameters such as strain, stress, and energy density. Three models—uniform deformation model (UDM), uniform deformation stress model (UDSM), and uniform deformation energy density model (UDEDM)—were employed to estimate these parameters. The UDM assumes isotropic properties, while UDSM and UDEDM consider anisotropic behavior. The results from these models showed different strain values, likely due to the anisotropic nature of the material. The mean particle size estimated from TEM, Scherrer’s formula, and W-H analysis was highly correlated. The root mean square (RMS) lattice strain was also calculated from interplanar spacing. The RMS strain linearly varied with the strain calculated from interplanar spacing, indicating no discrepancy on the (hkl) planes. The TEM image and selected area electron diffraction (SAED) patterns confirmed the nanocrystalline nature and wide size distribution of the ZnO nanoparticles. The Young's modulus (E) was calculated to be approximately 127 GPa, consistent with bulk ZnO. The three modified W-H models provided accurate and comparable results, making them suitable for determining the crystallite size and strain-induced broadening in ZnO nanoparticles.Zinc oxide (ZnO) nanoparticles were synthesized using the coprecipitation method at 450°C. X-ray diffraction (XRD) confirmed the formation of a wurtzite phase, and transmission electron microscopy (TEM) revealed spherical particles with an average grain size of about 50 nm. The crystalline size and lattice strain were evaluated using the Williamson-Hall (W-H) analysis, along with other physical parameters such as strain, stress, and energy density. Three models—uniform deformation model (UDM), uniform deformation stress model (UDSM), and uniform deformation energy density model (UDEDM)—were employed to estimate these parameters. The UDM assumes isotropic properties, while UDSM and UDEDM consider anisotropic behavior. The results from these models showed different strain values, likely due to the anisotropic nature of the material. The mean particle size estimated from TEM, Scherrer’s formula, and W-H analysis was highly correlated. The root mean square (RMS) lattice strain was also calculated from interplanar spacing. The RMS strain linearly varied with the strain calculated from interplanar spacing, indicating no discrepancy on the (hkl) planes. The TEM image and selected area electron diffraction (SAED) patterns confirmed the nanocrystalline nature and wide size distribution of the ZnO nanoparticles. The Young's modulus (E) was calculated to be approximately 127 GPa, consistent with bulk ZnO. The three modified W-H models provided accurate and comparable results, making them suitable for determining the crystallite size and strain-induced broadening in ZnO nanoparticles.