A method and arrangement are provided in connection with a continuous material web, which runs from an unwinder to a winder, at least one of which being a center winder. The method includes providing an initial value for density of a material on the center winder, calculating a moment of inertia for a roll of material on the center winder, determining tightness of the material web, producing a correction term for torque calculation based on a material web tightness reference, the material web tightness and the moment of inertia of the roll of material, calculating a torque reference based on the produced correction term and the calculated moment of inertia of the roll of material, and controlling the torque of the center winder based on the torque reference. The method also includes correcting the density value of the material on the center winder based on the produced correction term.