A method is described for measuring, in a multi-layer film obtained by blow extrusion process and formed by one or more layers of a first material and one or more layers of a second material, the total thickness (L1) of the first material and/or the total thickness (L2) of the second material, wherein the method comprises the steps of: a) acquiring by means of an X-ray sensor (16) a first measurement signal (Sx) representative of the total thickness of the film; b) acquiring by means of a capacitive sensor (18) a second measurement signal (Scap) which is the sum of the signals given by the first and second materials of the film, wherein the signal given by each material of the film is a function of the thickness (L1, L2) of said material; and c) calculating, from the first and second signals (Sx, Scap), the total thickness (L1) of the first material and/or the total thickness (L2) of the second material.