Abstract: Changes in atmospheric pressures may affect the calculation of volume of boil off gas (BOG) in LNG terminals to different extent depending on specific features of terminals. With consideration to different techniques deployed for control over pressures in storage tanks of different terminals, impacts of such changes are analyzed. The results show that, for LNG terminals where gauge readings of LNG storage tanks are used to control working loads of BOG compressors, drops in atmospheric pressures shall be considered during calculation of BOG volumes. It is especially true in terminals along costal areas that may experience frequent fluctuations in atmospheric pressures. For LNG terminals where absolute pressures of LNG storage tank are used to control working loads of BOG compressors, it is not necessary to consider changes in atmospheric pressures. Through comparison of techniques used in China and overseas for calculation of BOG, optimal calculation method is identified, providing important guidance to determine volume of BOG generated in LNG terminals and capacities of BOG compressors.