This document specifies a method for the determination of the bio-based carbon content in products, based on the 14C content measurement. This document 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: Liquid scintillation-counter (LSC); — method B: Accelerator mass spectrometry (AMS); and — method C: Saturated-absorption cavity ring-down (SCAR) spectroscopy. The bio-based carbon content is expressed by a fraction of sample mass or as a fraction of the total carbon content. This calculation method is applicable to any product containing carbon, including bio-composites. NOTE This document does not provide the methodology for the calculation of the biomass content of a sample, see EN 16785 1 and EN 16785 2.