BET is a great analysis to investigate the specific surface area, pore volume, pore diameter, and the mean of pore size of your product... depending on your material, the resulting specific surface area will be different; for example in porous organic polymers you can find specific surface areas upper than 500 m2/g.
You have to check your results with previously reported data in the litratures.
there is not same rang for all material. you must compare your data with previous studies and researches which were done in this field. the various parameters is important for example by the same material by the various synthesis method lead to the different results.