Method for cutting to size a tube fed in a longitudinal direction (X-X) to a winding machine equipped with a reel and at least one cutting blade, comprising the following steps: - equipping the winding machine with a sensor for detecting a marking on the tube, said sensor being mounted at a predefined distance D from the cutting blade; - providing, upstream of the winding structure, a unit for measuring the tube fed to the machine and comprising at least one metre-counting device and at least one marking device; - providing a control and operating device connected to the winding machine and to the measuring unit; - storing, in said control and operating device, predefined values for the length of the tube to be wound, the speed of movement of the tube fed for winding, and the relative distance D, in the longitudinal direction (X-X), between the device for reading the marking and the cutting blade; - operation of a device for feeding the tube to the measuring unit and to the winding machine at the predefined speed of movement; - fastening the tube onto the reel and starting the winding operation; - starting counting, by means of the metre-counting device, of the number of metres of tube fed; - emission, by the control and operating device, of a signal indicating that a predefined number of metres corresponding to the predefined length of tube to be wound has been reached; - sending the signal for the length reached and operation, by the control unit, of the marking device so as to apply a marking on the outer surface of the tube; - detection of the marking by the sensing device on the machine; - generating and sending, to the control unit, a signal for reading of the marking by the read device; - defining a time interval calculated as from emission of the signal for reading of the marking and defined on the basis of the distance between the marking reader and the cutting blade and the speed of movement of the tube; - operation of the cutting blade, by the control unit, at the end of said calculated time interval; - cutting the tube. - equipping the winding machine with a sensor for detecting a marking on the tube, said sensor being mounted at a predefined distance D from the cutting blade; - providing, upstream of the winding structure, a unit for measuring the tube fed to the machine and comprising at least one metre-counting device and at least one marking device; - providing a control and operating device connected to the winding machine and to the measuring unit; - storing, in said control and operating device, predefined values for the length of the tube to be wound, the speed of movement of the tube fed for winding, and the relative distance D, in the longitudinal direction (X-X), between the device for reading the marking and the cutting blade; - operation of a device for feeding the tube to the measuring unit and to the winding machine at the predefined speed of movement; - fastening the tube onto the reel and starting the winding operation; - starting counting, by means of the metre-counting device, of the number of metres of tube fed; - emission, by the control and operating device, of a signal indicating that a predefined number of metres corresponding to the predefined length of tube to be wound has been reached; - sending the signal for the length reached and operation, by the control unit, of the marking device so as to apply a marking on the outer surface of the tube; - detection of the marking by the sensing device on the machine; - generating and sending, to the control unit, a signal for reading of the marking by the read device; - defining a time interval calculated as from emission of the signal for reading of the marking and defined on the basis of the distance between the marking reader and the cutting blade and the speed of movement of the tube; - operation of the cutting blade, by the control unit, at the end of said calculated time interval; - cutting the tube.