A method to determine the mass flow rate of a low-pressure exhaust gas recirculation EGR circuit (EGR LP) of a supercharged internal combustion engine comprising an intake manifold, which receives a gas mixture through an intake pipe, and a turbocharger, which is provided with a turbine and with a supercharger arranged along the intake pipe; the low-pressure exhaust gas recirculation EGR circuit (EGR LP) comprises a bypass pipe originating from an exhaust duct downstream of the turbine and joining the intake pipe upstream of the turbocharger and an EGR valve; the supercharged internal combustion engine comprises, furthermore, an electronic control unit and a first sensor, which is designed to measure the quantity of oxygen available in the gas mixture flowing through the intake pipe; and a second sensor for measuring the temperature and the pressure of the gas mixture present in an intake manifold; the method comprises the steps of: detecting, by means of the first sensor, the percentage (O 2) of oxygen contained in the volume of the gas mixture flowing through the intake pipe; controlling the supercharged internal combustion engine so as to reduce to zero the mass flow rate of a low-pressure exhaust gas recirculation EGR circuit (EGR LP); determining the percentage (O 2_REF) of oxygen contained in the volume of fresh air coming from the outside that flows through the intake pipe through the formula O 2_REF =f(PSI AIR_IN,T AIR_IN) (); and determining a compensation factor (k), wherein the compensation factor (k) is variable as a function of the supercharging pressure in the intake pipe and is calculated as the ratio between the percentage (O 2_REF) of oxygen contained in the volume of fresh air coming from the outside that flows through the intake pipe and the percentage (O 2) of oxygen contained in the volume of the gas mixture flowing through the intake pipe, which is detected by means of the first sensor; controlling the supercharged internal combustion engine so as to feed a mass flow rate other than zero of a low-pressure exhaust gas recirculation EGR circuit (EGR LP) as soon as a given number of compensation factors (k) are learned; and determining the mass flow rate of the low-pressure exhaust gas recirculation EGR circuit (EGR LP) as a function of said compensation factor (k) through the formula R EGR =1-(k*O 2 /O 2_REF) (). the supercharged internal combustion engine comprises, furthermore, an electronic control unit and a first sensor, which is designed to measure the quantity of oxygen available in the gas mixture flowing through the intake pipe; and a second sensor for measuring the temperature and the pressure of the gas mixture present in an intake manifold; the method comprises the steps of: detecting, by means of the first sensor, the percentage (O 2) of oxygen contained in the volume of the gas mixture flowing through the intake pipe; controlling the supercharged internal combustion engine so as to reduce to zero the mass flow rate of a low-pressure exhaust gas recirculation EGR circuit (EGR LP); determining the percentage (O 2_REF) of oxygen contained in the volume of fresh air coming from the outside that flows through the intake pipe through the formula O 2_REF =f(PSI AIR_IN,T AIR_IN) (); and determining a compensation factor (k), wherein the compensation factor (k) is variable as a function of the supercharging pressure in the intake pipe and is calculated as the ratio between the percentage (O 2_REF) of oxygen contained in the volume of fresh air coming from the outside that flows through the intake pipe and the percentage (O 2) of oxygen contained in the volume of the gas mixture flowing through the intake pipe, which is detected by means of the first sensor; controlling the supercharged internal combustion engine so as to feed a mass flow rate other than zero of a low-pressure exhaust gas recirculation EGR circuit (EGR LP) as soon as a given number of compensation factors (k) are learned; and determining the mass flow rate of the low-pressure exhaust gas recirculation EGR circuit (EGR LP) as a function of said compensation factor (k) through the formula R EGR =1-(k*O 2 /O 2_REF) (). detecting, by means of the first sensor, the percentage (O 2) of oxygen contained in the volume of the gas mixture flowing through the intake pipe; controlling the supercharged internal combustion engine so as to reduce to zero the mass flow rate of a low-pressure exhaust gas recirculation EGR circuit (EGR LP); determining the percentage (O 2_REF) of oxygen contained in the volume of fresh air coming from the outside that flows through the intake pipe through the formula O 2_REF =f(PSI AIR_IN,T AIR_IN) (); and determining a compensation factor (k), wherein the compensation factor (k) is variable as a function of the supercharging pressure in the intake pipe and is calculated as the ratio between the percentage (O 2_REF) of oxygen contained in the volume of fresh air coming from the outside that flows through the intake pipe and the percentage (O 2) of oxygen contained in the volume of the gas mixture flowing through the intake pipe, which is detected by means of the first sensor; controlling the supercharged internal combustion engine so as to feed a mass flow rate other than zero of a low-pressure exhaust gas recirculation EGR circuit (EGR LP) as soon as a given number of compensation factors (k) are learned; and determining the mass flow rate of the low-pressure exhaust gas recirculation EGR circuit (EGR LP) as a function of said compensation factor (k) through the formula R EGR =1-(k*O 2 /O 2_REF) ().