This International Standard specifies methods for calculating the resin, fibre and void contents of a carbon-fibre-reinforced composite from the densities of the resin, the fibre and the composite and the mass of fibre in the composite (method A) and for calculating the fibre content from the thickness of the composite (method B).Method A specifies three different resin removal procedures for the determination of the mass of fibre in the composite (viz a combustion procedure, a procedure by digestion in nitric acid and a procedure by digestion in a mixture of sulfuric acid and hydrogen peroxide). The selection of the procedure to be used is made by considering the combustibility of the resin used in the composite, its ability to decompose and the type of resin concerned. It should be noted that method A is only of limited applicability when filled resins are present that could prevent complete dissolution and/or combustibility of the resin. Method B (thickness measurement method) is only applicable to composites moulded from prepregs of known fibre mass per unit area.