This document specifies a method of determining the length of the fibres present in a fibre-reinforced product. The method is applicable to moulding materials and to moulded parts. The test conditions specified limit the application of this method to thermoplastics reinforced with short glass fibres (less than 1 mm long), i.e. fibres whose length is less than or equal to 7,5 mm prior to incorporation in the moulding material and moulding.