A measurement is presented of the $\mathrm {Z}/\gamma ^{} \rightarrow \tau \tau $ cross section in $\text {pp}$ collisions at $\sqrt{s} = 13\hbox { TeV}$ , using data recorded by the CMS experiment at the LHC, corresponding to an integrated luminosity of $2.3\hbox { fb}^{-1}$ . The product of the inclusive cross section and branching fraction is measured to be $\sigma (\text {pp} \rightarrow \mathrm {Z}/\gamma ^{}\text {+X}) , \mathcal {B}(\mathrm {Z}/\gamma ^{*} \rightarrow \tau \tau ) = 1848 \pm 12,(\text {stat}) \pm 67\text { (syst ,+,lumi)}\text { pb} $ , in agreement with the standard model expectation, computed at next-to-next-to-leading order accuracy in perturbative quantum chromodynamics. The measurement is used to validate new analysis techniques relevant for future measurements of $\tau $ lepton production. The measurement also provides the reconstruction efficiency and energy scale for $\tau $ decays to hadrons $,+,\nu _{\tau }$ final states, determined with respective relative uncertainties of 2.2 and 0.9%.