Display omitted •13C CP-MAS NMR can be used to reliably quantify the composition of cellulose and polyester in textile blends.•Sigmoidal calibration functions describe the correlation between cellulose and polyester signals in the NMR spectrum.•It is also possible to apply solid-state NMR to determine the crystallinity of cellulose in cotton polyester blended textiles. The valorization of cellulose rich textile waste is promoted by the development of a novel solid-state NMR method for the quantification of cellulose and polyester in textile blends. We applied 13C CP-MAS NMR as a tool for the quantification and structural characterization of cellulose in cotton polyester blends. Gaussian functions were used to integrate the spectra obtained from a set of calibration standards in order to calculate a sigmoidal calibration curve. Acid hydrolysis was chosen as a reference method. The results demonstrated that solid-state NMR enables a reliable determination of cellulose and polyester in both preconsumer and postconsumer waste textiles and suggests a possible extension of the concept to blends of man-made cellulose fibers (MMCFs) and polyester.