Calculation of nominal fixed grid, aimed to project a given area of the earth to the nominal image, is a key technique for navigation and registration of geostationary satellites. In view of the existing nominal fixed grid definitions from coordination group for meteorological satellites (CGMS) specification and geostationary operational environmental satellite-R series (GOES-R) user's guide, whose representatives are FY-4A, Himawari-8, MTG, Electro-L satellites and GOES-R satellite, respectively, the formulas of CGMS and GOES-R nominal fixed grid calculation are deduced in detail, and the difference and relationship between CGMS and GOES-R nominal grids are summarized. Both nominal fixed grids are defined in satellite body Cartesian coordinate system. Furthermore, the detailed transforming process from nominal image of CGMS specification to the corresponding nominal image of GOES-R definition is presented using FY-4A observations. The results demonstrate that the nominal images defined by the two aforementioned methods can be converted to each other. Besides, by comparing the scanning and stepping angles of FY-4A advanced geosynchronous radiation imager to the responding angles of GOES-R fixed grid, the differences are 10 -16 μrad and 10 -17 μrad magnitude, respectively, which reveals that GOES-R fixed grid is defined from the point view of opto-mechanical design of advanced base imager. Considering that the foreign satellites, except GOES-R, all use CGMS fixed grid to calculate the nominal image, for end-user's convenience, FY-4A nominal fixed grid will adopt the internationally accepted standard projection defined in CGMS LRIT/HRIT global specification.