This Technical Specification specifies a calculation method for the determination of the bio-based carbon content in monomers, polymers and plastic materials and products, based on the 14C content measurement. It also specifies three test methods to be used for the determination of the 14C content from which the bio-based carbon content is calculated: Method A: Proportional scintillation-counter method (PSM); Method B: Beta-ionisation (BI); Method C: Accelerator mass spectrometry (AMS). The bio-based carbon content is expressed by a fraction of sample mass, as a fraction of the total carbon content or as a fraction of the total organic carbon content.This calculation method is applicable to any polymers containing organic carbon, including biocomposites. NOTEThis Technical Specification does not provide the methodology for the calculation of the biomass content of a sample.