In the USA, dry sieving (ASTM D 4751) is an approved and commonly used method to measure the apparent opening size, O95 (AOS) of geotextiles. Although capillary flow porometry (ASTM D 6767) was approved in 2002, it is still not widely adopted, despite it provides the largest pore size (O98) and a complete pore size distribution of a geotextile. The Capillary flow porometry is exempt of most of the experimental issues which affect the repeatability and precision of Dry Sieving test, such as the impact of electrostatic effects and clogging of glass beads within the geotextile. Many soil retention criteria currently used are based on AOS values of geotextiles. Therefore, researchers have been trying to come up with a correlation factor between dry sieving and capillary flow test results. However, different relationships have been established till now due to the limited number of geotextiles used in the various studies, lack of proper calibration and use of equipment with inappropriate ranges of precision. The goal of this study is to compare the results of calibration at three different laboratories using similar materials, wetting liquid and ASTM standard but two different porometers. In addition, six woven and non-woven geotextiles were included in the study to compare capillary flow and dry sieving test results.