The paper covers a preliminary-draft selection of geometrical parameters in external and internal spur and helical automotive gearboxes. A special convention of signs for geometrical parameters in internal gears is introduced (11)*, owing to that convention all the geometrical formulas are the same for the external and internal gears. The preliminary draft selection of centre distance and face-width is given according to the calculated torque, contact stress factor kH, gear ratio u and relationship of facewidth to the centre distance of gearbox. The number of teeth according to gear ratio u and relationship of bending stress factor kF to contact stress factor kH for case-hardened steel is given. The example is given based on actual construction of gearbox produced in Poland.