The objective of the Norfor structure system was to establish a model for prediction of eating- (EI), ruminating- (RI) and total chewing index (CI) for feeds and total rations fed to dairy cows. The model was predicted from a Meta analysis of more than 100 published experiments including results on eating, ruminating and total chewing time by cattle fed mainly high forage diets. The EI is proportional with the neutral detergent fibre (NDF) content and a particle size factor (Size_E) of the feed. The RI is proportional with the NDF content, a particle size factor (Size_R) and a hardness factor of the feed. The CI is estimated as the sum of the EI and RI. The Size_E and Size_R values are estimated from exponential functions of the most frequent particle length. The hardness factor is estimated as a linear function of the proportion of indigestible NDF in NDF. A minimum dietary CI value of 32 minutes per kg of total DMI is considered to ensure a sufficient intake of physically effective fibre in order to ensure good ruminal fibre digestion and to prevent a low rumen pH, digestive disorders and a low milk fat content in high-yielding dairy cows.