Using adsorption data, we get formulas for the calculation of fractal dimensions : log [A((CO2)(DP))/A(N2(BET))] = -5.3984(2 - D-1)/2 and log[A(CO2(BET))/A(N2(BET))] = -4.9569(2 - D-2)/2. The fractal dimensions (D) of 27 coals and 2 cokes have been obtained. The D of coals decreased with the increase of f(a) and reached a maximum at H/C equal to 0.66 (or C-daf about 86%). The fractal dimension is relative to ash and volatiles of coal : D = 2.2237 + 0.6249V(daf) + 0.8863A(d). The relationship between D of coal coke and its conversions (X) obeys the following equation : D = a exp(-bX) + c.