The aim of this work was to validate that isotropic deformation theory of plasticity is a suitable material modelling level for fracture mechanics analysis of paper materials, as has been indicated in previous studies. Six different commercial paper grades were investigated. Laboratory material testing was performed for each paper grade using standardised tensile and fracture toughness test methods. The material data was used to calibrate a fracture mechanics model based on isotropic deformation theory of plasticity with a fracture criterion based on the/-integral. The fracture mechanics model was used to predict failures of notched paper webs and corresponding experiments were performed. The experiments and predictions of failures were performed for several different notch lengths for all six studied paper materials. The experimentally determined force and elongation at break of the notched paper webs were predicted excellently by the fracture mechanics model, which shows that isotropic deformation theory of plasticity is a suitable material modelling level for fracture mechanics analysis of paper materials.