Precision measurement of luminosity delivered by the LHC to the CMS experiment is a vital component of many physics analyses and important for optimal machine performance. In Run 2, the luminosity at CMS is measured by three online luminometers, the Pixel Luminosity Telescope (PLT), Fast Beam Conditions Monitor (BCM1F), and the hadronic forward calorimeter (HF), which provide high-precision real-time luminosity measurements. They are complemented by two offline measurements, one using pixel cluster counting (PCC) in the main CMS pixel detector, and one using the rate of muon stubs in the drift tubes (DT). In order to calibrate the luminosity measurements, a series of van der Meer (VdM) scans is performed, in which the absolute luminosity can be calculated to determine a calibration. In the VdM scans, the separation of the beam is varied and the resulting profile of luminosity as a function of separation is fitted in order to determine the beam overlap width, from which the overall luminosity can be calculated. This analysis presents the results of this calibration, as well as the various systematic effects taken into account in the measurement.