Method for estimating the mass enclosed in the combustion chamber of a cylinder of a motor vehicle internal combustion engine, equipped with a means for measuring the pressure in the cylinder, a means for measuring the crankshaft angle with respect to a reference position and the temperature of the combustion chamber coolant, the method comprising steps during which: the rotational speed of the engine is determined from the crankshaft angle measurement, the engine load is determined, characterized in that it comprises the following steps: when the valves of the cylinder are fully closed and before the first injection of fuel, the volume of the cylinder is determined as a function of the crankshaft angle, calibration parameters associated with the heat losses at the walls are determined as a function of a map that is a function of the rotational speed of the engine, the modelled temperature in the cylinder is determined using a nonlinear dimensionless model of the pressure and the temperature in the combustion chamber, as a function of the cylinder pressure measurement, the specific gas constant for the gases in the cylinder, the specific heat at constant volume of the gases in the cylinder, the volume of the combustion chamber and calibration parameters associated with the heat losses at the walls, and the estimate for the mass enclosed in the cylinder is determined as a function of the modelled temperature in the cylinder and the measurement of cylinder pressure. the rotational speed of the engine is determined from the crankshaft angle measurement, the engine load is determined, characterized in that it comprises the following steps: when the valves of the cylinder are fully closed and before the first injection of fuel, the volume of the cylinder is determined as a function of the crankshaft angle, calibration parameters associated with the heat losses at the walls are determined as a function of a map that is a function of the rotational speed of the engine, the modelled temperature in the cylinder is determined using a nonlinear dimensionless model of the pressure and the temperature in the combustion chamber, as a function of the cylinder pressure measurement, the specific gas constant for the gases in the cylinder, the specific heat at constant volume of the gases in the cylinder, the volume of the combustion chamber and calibration parameters associated with the heat losses at the walls, and the estimate for the mass enclosed in the cylinder is determined as a function of the modelled temperature in the cylinder and the measurement of cylinder pressure. when the valves of the cylinder are fully closed and before the first injection of fuel, the volume of the cylinder is determined as a function of the crankshaft angle, calibration parameters associated with the heat losses at the walls are determined as a function of a map that is a function of the rotational speed of the engine, the modelled temperature in the cylinder is determined using a nonlinear dimensionless model of the pressure and the temperature in the combustion chamber, as a function of the cylinder pressure measurement, the specific gas constant for the gases in the cylinder, the specific heat at constant volume of the gases in the cylinder, the volume of the combustion chamber and calibration parameters associated with the heat losses at the walls, and the estimate for the mass enclosed in the cylinder is determined as a function of the modelled temperature in the cylinder and the measurement of cylinder pressure.