The cell group constants in a light water moderated reactor have been computed to many lattice parameters, such as fuel rod diameter, lattice pitch, isotopic content, moderator density, temperature, These group constants are found to be able to be fitted by such limited new variables as moderator-to-fuel-volume ratio, fuel optical length, and so on. By this expression, the number of fitting coefficients to be conserved for cell calculation becomes small. The fitting coefficients are summarized in a table called the “Few-Group Constants Table” (FG-Table). By using this table, many kinds of cell constants, such as burnup- or moderator-density-dependent constants, become easy to obtain. To check the reliability of the present approach, calculated values with the table are compared with zero power experimental data, which show a good agreement with each other.