Master curve and reference temperature (T₀) from three-point bending specimens of 20MnMoNi55 steel for different thicknesses and a/W ratios are determined using Kim Wallin’s master curve methodology (ASTM E1921-02) to study the effect of variation in thickness and a/W ratio at reference temperature (T₀). Weibull stress at the crack tip is calculated from FE analysis of each fracture test using FE software ABAQUS. Calibration of Beremin parameters, like Weibull modulus (m) and scaling parameter (σ_u), and C_m,n is done using linear regression analysis of a large number of fracture test data at single test temperature. T₀ for different thicknesses and a/W ratios are also evaluated from corresponding Weibull stress based on Beremin model using calibrated m, σ_u and C_m,n which are compared with experimental results showing case-specific good matching. The same calibrated values of Beremin parameters and C_m,n are also used to evaluate T₀ for CT specimen of the same material using Beremin model, and an excellent matching with the experimental result is found.