An equation for the net volume estimation of ‘Lenga’ forests (Nothofagus pumilio, Poepp. et Endl. Krasser) was designed. This function gives highly consistent results and is based on a large number of sample trees obtained by a selective cutting method called ‘floreo,’ which is similar to the traditional method used by local woodsmen. The equation has been successfully employed to estimate the net volume of species for the Chubut Province native forest inventory.