1. A method for operating a turbo charger for a combustion engine, comprising the steps of: providing a set of values of a basic boost pressure for opening a waste gate for the turbo charger being derived at standard conditions comprising a standard temperature and at a standard pressure; measuring an ambient air temperature using a temperature sensor; measuring an ambient air pressure using a pressure sensor; calculating a density of ambient air at least using the ambient air temperature and the ambient air pressure; transforming at least one point of the set of values of the basic boost pressure at the standard conditions into at least one point of an estimated set of values of the basic boost pressure at ambient conditions by a correction factor based on the density; and using at least one estimated value of the estimated set of values of the basic boost pressure to control the waste gate of the turbo charger.