The protein contents of diet meals containing various foods were calculated from the total nitrogen content using novel conversion factors that were suggested in our previous reports. Focusing on school lunch menus and convenience store lunch boxes, the total nitrogen contents in these foods were calculated by dividing the protein contents referring to the Standard Tables of Foods Composition in Japan by the traditional N : P factors. The total nitrogen content multiplied by the novel N : P factor was equal to the novel protein content.   The proportion of novel protein contents to the traditional protein contents was approximately 84%. On 11 school lunch menus, the equation between traditional protein contents and novel protein contents was the following : Novel protein contents=0. 878 × traditional protein contents–0. 937. The novel protein content of a convenience store lunch box could be estimated by this regression equation. The novel N : P factor, that is, the ratio of nitrogen contents to novel protein contents, for school lunch menus was 5. 16±0. 11 (mean±standard deviation). The N : P factors for two convenience store lunch boxes were 5. 15 and 5. 09. Therefore, the protein content of well-balanced meals should be calculated using the novel N : P factor of about 5. 2.   The results indicated that the novel calculation method for N : P factors could be applied to not only individual foods, but also to diet menus containing various foods. We conclude that this calculation method should be practical and suitable for the evaluation of the N : P factors.