In situ X-ray crystallography powder diffraction studies on beta silicon carbide (3C-SiC) in the temperature range 25�800 °C at the maximum peak (111) are reported. At 25 °C, it was found that the lattice parameter is 4.596 à , and coefficient thermal expansion (CTE) is 2.4 � (Formula presented.) /°C. The coefficient of thermal expansion along a-direction was established to follow a second order polynomial relationship with temperature (Formula presented.)). CASTEP codes were utilized to calculate the phonon frequency of 3C-SiC at various pressures using density function theory. Using the Gruneisen formalism, the computational coefficient of thermal expansion was found to be 2.2 � (Formula presented.) /°C. The novelty of this work lies in the adoption of two-step thermal expansion determination for 3C-SiC using both experimental and computational techniques. © 2022 by the authors.