A force-displacement trace of a Charpy impact test of a reactor pressure vessel (RPV) steel in the transition range has a characteristic point, the so-called “force at the end of unstable crack propagation,” Fa. A two-parameter Weibull probability function is used to model the distribution of the Fa in Charpy tests performed at Oak Ridge National Laboratory (ORNL) on different RPV steels in the unirradiated and irradiated conditions. These data have a good replication at a given test temperature, thus, the statistical analysis was applicable. It is shown that when temperature is normalized to TNDT, using (T - TNDT), or to T100a using (T - T100a), the median Fa values of different RPV steels have a tendency to form the same shape of temperature dependence. Depending on normalization temperature, TNDT or T100a, the results suggest a universal shape of the temperature dependence of Fa for different RPV steels. The best fits for these temperature dependencies are presented. These dependencies are suggested for use in estimation of nil-ductility transition (NDT) or T100a from randomly generated Charpy impact tests. The linear least squares and maximum likelihood methods are used to derive equations to estimate TNDT and T100a from randomly generated Charpy impact tests.