The stacking-faults are placed in a supercell which is repeated periodically. By choosing the supercell large enough, so that faults in neighboring cells do not interact much, the energy of one stacking fault may then be calculated. A first principle method (Augmented Spherical Wave Method) is used to calculate the energies of the intrinsic and extrinsic stacking faults in aluminium. The values found are ΓISF=154erg/cm2 and ΓESF=138erg/cm2 respectively. The results are quite reasonable as compared with experimental data.