Abstract: The present invention relates to a method for determining a thickness of a tree trunk (17) in a harvesting head (1) for forestry, said harvesting head (1) comprising a tree trunk pressing device (3, 4, 7, 8), and a tree trunk surface follower (11, 11), wherein the tree trunk surface follower is a limbing member (11, 11?), and wherein the limbing member (11, 11?) is curved, said method comprising pressing the tree trunk (17), with said tree trunk pressing device (3, 4, 7, 8), in a direction towards a reference surface (15) of the harvesting head (1) and determining a measured thickness (T) by measuring the position of the tree trunk pressing device (3, 4, 7, 8) and relating said position to said reference surface (15), said method further comprising the steps of determining a deviation (D) of the tree trunk (17) from said reference surface (15) by measuring a position of the tree trunk surface follower (11, 11?) and relating said position of the tree trunk surface follower (11, 11?) to said reference surface (