A method for determining a quantity of air within a cylinder of an internal combustion engine includes the steps of scaling an intake manifold pressure and an exhaust gas pressure in dependence on an actual ambient air pressure and a standard ambient air pressure in order to provide a scaled intake manifold pressure and a scaled exhaust gas pressure, implementing an air charge calculating algorithm produced under a standard ambient air pressure operating condition, in order to determine a standard quantity of air based on the scaled intake manifold pressure and the scaled exhaust gas pressure, and scaling the standard quantity of air in dependence on the actual ambient air pressure and the standard ambient air pressure in order to calculate the quantity of air within the cylinder of the internal combustion engine. An engine control unit and a method for controlling an internal combustion engine are also provided.