This paper investigates on the contribution of hemicelluloses, cellulose, and lignin to the carbon mass and the textural properties of activated carbons produced from lignocellulosic precursors by phosphoric acid activation. Four raw materials (olive pomace, miscanthus, tomato plants, and poplar wood) were tested. Nitrogen adsorption-desorption at 77 K was used to determine the porous properties of chars and activated carbons produced from the biomass residues studied. A predictive calculation, based on the biochemical composition of the raw materials, was studied to evaluate the heat treatment yields without and with the activating agent and the respective contributions of hemicelluloses, cellulose, and lignin to the chars and to the subsequent activated carbons of various precursors in terms of carbon weight fraction. The results of this calculation were compared with the experimental ones. This study shows that the contribution (in carbon mass %) of hemicellulose, cellulose, and lignin in the final activated carbons after a phosphoric acid activation is very close to the biochemical composition of the lignocellulosic precursor. It was also found that lignin is responsible for the microporous domain in the activated carbon in contrast with hemicelluloses and cellulose which are responsible for the formation of the mesoporous domain.