A measurement of the production cross-section of Z bosons in pp collisions at s√=13s=13 TeV is presented using dimuon and dielectron final states in LHCb data. The cross-section is measured for leptons with pseudorapidities in the range 2.0 < η < 4.5, transverse momenta p T > 20 GeV and dilepton invariant mass in the range 60 < m(ℓℓ) < 120 GeV. The integrated cross-section from averaging the two final states is σ Z ℓℓ  = 194.3 ± 0.9 ± 3.3 ± 7.6 pb, where the first uncertainty is statistical, the second is due to systematic effects, and the third is due to the luminosity determination. In addition, differential cross-sections are measured as functions of the Z boson rapidity, transverse momentum and the angular variable ϕ η * .