CMS luminosity measurement for the 2018 data-taking period at $\sqrt{s} = 13~\mathrm{TeV}$

The calibration of the luminosity measurement by the CMS experiment in the 2018 proton-proton data taking at $\sqrt{s} = 13~\mathrm{TeV}$ is described. The principal calibration is derived from the analysis of the van der Meer scan program in CMS taken during LHC fill 6868. In addition, the performance and stability of the CMS luminometers are also evaluated using emittance scans taken throughout the course of the year. The systematic uncertainty in the absolute calibration from the van der Meer scan is derived with a precision of $2.1\%$, with the dominant contribution to the uncertainty arising from the $x$-$y$ nonfactorization of the beam shape. The total systematic uncertainty, including terms from stability and linearity effects, is $2.5\%$.