Abstract The improvement of the natural fibers which are used in composite materials engineering applications depends on the reliable estimation of their mechanical properties, whose calculation is directly associated with the determination of their physical characteristics, such as cross-sectional area and diameter. The cross-sectional area of fique yarns, a natural fiber obtained from “furcraea andina” plant, consists in the sum of several singular fiber areas packaged thanks to the torsion effect of the spinning process. In this study, cross-sectional areas of fique yarns were obtained by optical micrographs, afterwards, the images were processed by two different approaches: the first one using Fiji, a specialized software for image processing; and the second one, through an own Matlab programming. The results obtained by both methods were compared and the respective diameter values for each fiber were extracted, assuming a circular shape of fique fibers cross-section. To perform the microscopic shots, fique yarns (0,877 and 0,714 tex) with torsion degrees of 1.5, 2.0 and 2.5 turns/inch were selected. The results indicated that even though linear density remain constant, the cross-sectional area varies with torsion degree. Additionally, the image analysis method allowed to improve the accuracy of calculations. It is expected that the measurement method proposed contributes to improving mechanical analysis of these type of materials in future studies.