A method based on fractal geometry is suggested to simulate the porous structure of calcined limestone, in which a model similar to the Menger sponge is employed for the porous calcine. The bulk fractal dimension is calculated on the basis of the experimentally obtained pore-size distribution density. The effects of various factors (such as particle size, calcination temperature and environment, etc.) on the porous structure (i.e. on its bulk fractal dimension) are studied. Combined with the results of sulfur-removal experiments and theoretical analysis, it is concluded that optimum utilization will be achieved when limestone is calcined to a structure with bulk fractal dimensions between 2.53 and 2.65. This fractal dimension is calculated under normal conditions and may provide an alternative ranking index for calcium-based sorbents.