A measurement of the tt production cross section at √s = 13TeV is presented using proton-proton collisions, corresponding to an integrated luminosity of 2.2 fb^-1, collected with the CMS detector at the LHC. Final states with one isolated charged lepton (electron or muon) and at least one jet are selected and categorized according to the  accompanying jet multiplicity. From a likelihood t to the invariant mass distribution of the isolated lepton and a jet identied as coming from the hadronization of a bottom quark, the cross section is measured to be σ_tt = 888 ± 2; (stat)⁺²⁶ _-28 (syst)  ± 20 (lumi) pb, in agreement with the standard model prediction. Using the expected dependence of the cross section on the pole mass of the top quark (m_t), the value of m_t is found to be 170:6 ± 2:7 GeV.