A new application of geosynthetic tube for offshore dike construction is geosynthetic mattress in which its horizontal dimension is much greater than the vertical one. This makes it more stable than the sausage shaped geosynthetic tube. However, the existing analytical or numerical methods developed for the sausage shaped geosynthetic tube may not be applicable directly to geosynthetic mattresses as the solution may not converge. In this paper, a closed-form solution was derived for a direct determination of the cross-section of geosynthetic mattress. Laboratory large scale model tests were also carried out to verify the proposed analytical method. The cross-sections of the geosynthetic mattresses obtained from the closed-form solutions agreed well with the data obtained from model tests. The tensile forces measured from the model tests were rather scattered but showed a consistent thread as those from the closed-form solutions. (C) 2013 Elsevier Ltd. All rights reserved.