Top mass measurement at LHC

The Large Hadron Collider (LHC) will be a top factory, since about 8 millions of ttbar events will be produced in one year of running at low luminosity. This large amount of data will allow an accurate measurement of the top quark mass, with a precision at the level of 1 GeV, dominated by systematic uncertainties. The physics goals of this accuracy will be recalled. The principle of this measurement in all dominant decay channels of the ttbar production will be described. The estimation of the main systematic uncertainties (energy scale, final state radiation) in these several channels, assuming nominal running conditions, will be given.