W mass measurement in the ATLAS experiment

A precise measurement of the mass of the W boson will be essential to provide improved indirect constraints, e.g. on the Higgs boson mass. Using new methods developed for this challenging measurement, the performance expected is presented, evaluating various sources of systematic uncertainties, both of experimental and theoretical nature. The focus of this contribution will be on the expectation for the initial data taking and results will be shown for an integrated luminosity of 15 pb-1. Prospects on the total uncertainties which may be obtained with an integrated luminosity of 10 fb-1 will be given.