In this paper, an attempt is made to analyse the dilative behaviour of dense sand at two different sizes of the direct shear box, i.e., small (60 mm × 60 mm ×30 mm) and large (305 mm × 305 mm × 140 mm). A three-dimensional numerical model is developed using the FLAC3D software to analyse the size effect on dilative behaviour of dense sand along the top and the shear plane of the box at 15 kPa normal pressure. It is observed that the vertical deformation of soil on top plane increases linearly with horizontal displacement, whereas on shear plane, the vertical deformation remains constant after yielding of sand. It is also found that there is greater movement of sand particles at the front and the back of the box for the large shear box compared with that for the small shear box. © Springer Nature Singapore Pte Ltd 2019.