The scatter in tensile properties induced by the determination and calculation method of the cross-sectional area (CSA) of bast fibre bundles is almost as high as the scatter found in the literature. Different methods (light microscopy, high resolution flat-bed scanning, and laser-based fibre dimensional analysis) were applied to exactly the same flax fibre bundles prior to tensile testing, and different approaches for the calculation of the CSA were applied. The CSA method alone is introducing up to 300 % of variation in tensile strength data. These results show that there is a strong need for standards and standardisation of fibre bundle testing. Care has to be taken when comparing results from studies using slightly different methods.