# Setting the Number of Cells¶

Together with the grid resolution in grid.param, the number of cells in our .cfg files determine the overall size of a simulation (box). The following rules need to be applied when setting the number of cells:

Each GPU needs to:

1. contain an integer multiple of supercells
2. at least three supercells

Supercell sizes in terms of number of cells are set in memory.param and are by default 8x8x4 for 3D3V simulations on GPUs. For 2D3V simulations, 16x16 is usually a good supercell size, however the default is simply cropped to 8x8, so make sure to change it to get more performance.