Electroweak results at LHCb

$W$ and $Z$ production cross-sections have been measured in proton-proton collisions at a center-of-mass energy of 7 TeV using the decays $W\rightarrow \mu \nu$, $Z \rightarrow \mu \mu$ and $Z \rightarrow \tau \tau$ collected by the LHCb detector. For all the measurements at least one of the reconstructed muons has a transverse momentum, $p_T$, above 20 GeV/$c$ and a pseudorapidity, $\eta$, between 2 and 4.5. In the case of the $Z$, a di-muon invariant mass between 60 GeV$/c^2$ and 120 GeV$/c^2$ is required. Theoretical predictions, calculated at next-to-next-to-leading order in QCD using recent parton distribution functions (PDFs), are found to be in agreement with the measurements.