The master curve methodology proposed by Kim Wallin (ASTM E1921-02) has been used to evaluate master curve and reference temperature (T₀) from TPB specimen for the material 20MnMoNi55 steel using single temperature and multitemperature method. The effect of test temperature on reference temperature (T₀) has been studied for both TPB and CT specimens. A study is performed on the censor parameter M for both TPB and CT specimen and a correction value is suggested for TPB specimen for the material 20MnMoNi55 steel. To study the effect of constraint ( a/w and thickness ) on reference temperature (T₀), the value of (T₀) is calculated for different a/w ratio and thickness of TPB specimen. The results are compared with the results obtained from CT specimen for the same material to study the effect of geometry on reference temperature (T₀).