With the high integrated luminosities recorded at the LHC and the very good understanding of the ATLAS detector, it is possible to measure electroweak observables to the highest precision. In this talk, we present the tau polarisation, measured in $Z\to \tau\tau$ using 20.3 fb$^{-1}$ of proton proton collision data collected at a centre of mass energy of 8 TeV. The talk also reviews the measurement of forward-background asymmetry based on the triple differential Drell-Yan cross-section obtained with the same data sample, which can be used to extract the weak mixing angle. We conclude with a presentation of the measurement of the $W$-boson mass using 4.6 fb$^{-1}$ data, collected at 7 TeV.