Assessment of the structural safety of masonry buildings cannot be independent of knowledge of the material mechanical properties. Among the mechanical parameters of masonry, the elastic modulus plays a fundamental role in modeling and evaluating the performance of masonry buildings. It is commonly determined by in situ tests performed with double flat jacks in accordance with American codes RILEM TC 177-MDT.D.5 and ASTM C1197. This work analyzes the results of a significant number of tests with double flat jacks performed on the masonry of historic buildings to determine their elastic modules following the procedures provided by codes and those reported in the literature. The results obtained are compared with the values of the elastic modules reported in Circular n. 7 of 2019 to better evaluate the reliability of the different procedures.