Precise top quark cross-section results at LHC

The measurements of the inclusive $t\bar{t}$ cross section is presented for proton-proton collisions recorded at $\sqrt{s}=$ 7 and 8 TeV by the ATLAS and the CMS experiments using the lepton+jets and the dilepton events. The most precise single measurement at 7 TeV is $\sigma_{t\bar{t}} = 161.9\pm2.5$(stat.)$^{+5.1}_{-5.0}$(syst.)$\pm3.6$(lumi.)pb, using a luminosity of 2.3fb$^{-1}$. The measurements from the two experiments are also combined to reach higher precision. With a luminosity of about 1fb$^{-1}$, the combined cross-section is $\sigma_{t\bar{t}}$ = 173.3$\pm$2.3(stat.)$\pm$9.8(syst.)pb. At $\sqrt{s}=$8 TeV, $\sigma_{t\bar{t}}$ is measured in the lepton+jets and dilepton channels with the CMS detector and the corresponding combined measurement is $\sigma_{t\bar{t}} = 227\pm3$(stat.)$\pm11$(syst.)$\pm10$(lumi.)pb.