The present invention relates to a method for determining the rotational speed of the main shaft (3) of a transmission in which the main shaft (3) is connected to an output shaft (4) via a shiftable planetary gear (17), whereby the main shaft (3) is connected in a rotationally fixed manner to the sun gear (18) and the output shaft (4) is connected in a rotationally fixed manner to the planet carrier (20). The steps of the method are picking up the rotational speed (n.sub.Hohlrad) of the ring gear (22), picking up the rotational speed (n.sub.Abtrieb) of the output shaft or the planet carrier (20), and computing the rotational speed (n.sub.Hauptwelle) of the main shaft (3) from the rotational speed (n.sub.Hohlrad) of the ring gear and the rotational speed (n.sub.Abtrieb) of the output shaft or the planet carrier (20). The present invention further relates to a transmission having a rotational speed pickup device.