Geotextile tubes are severally used more and more in maritime field as systems of beaches protection against coastal erosion. The prediction of their dimensions is very important, because these they govern the stability against several site conditions of wave and current. There are many studies that have calculated the dimensions of geotextile tubes, but they require the running of a computer program and this limits their access to a larger public of designers. The most popular one is the approach presented by Leshchinsky and the computer program GeoCoPS 2.0. In this paper, and in addition to the approach established by Amallas and Ajdor 2018, another numerical approach is established in order to calculate definitively dimensions of geotextile tubes regarding the pumping pressure P0 (kPa) and the material density γ (kN/m3). The most useful formulas for the direct calculation of filled geotextile tube dimensions, depending on P0 (kPa), material density γ (kN/m3) and the circumference of tube L (m) are given for the large public designers without further resort to have computer programs. The comparison between values calculated by these formulas, the ones given by the established program and the ones given by the existing methods, highlights a very good agreement.