The mass of the Higgs boson is measured in the H → ZZ∗→ 4 and in the H → γγ decay channels with 36.1 fb−1of proton–proton collision data from the Large Hadron Collider at a centre-of-mass energy of 13 TeV recorded by the ATLAS detector in 2015 and 2016. The measured value in the H → ZZ∗→4 channel is mZZ∗H=124.79 ±0.37 GeV, while the measured value in the H → γγ channel is mγγH=124.93±0.40 GeV. Combining these results with the ATLAS measurement based on 7 and 8TeVproton–proton collision data yields a Higgs boson mass of mH=124.97 ±0.24 GeV.