Expected pileup values at the HL-LHC

In this brief note the expected mean number of interactions and the length of the luminous region for the HL-LHC is discussed for an instantaneous luminosity of $5 \times 10^{34} /{\rm cm}^2/{\rm s}$. Its dependence on various parameters is discussed and an uncertainty is estimated. It is found that the mean pileup is about 128, and up to 16\% of all bunches will have a pileup of $> 140$. The length of the luminous region is anticipated to be about 5 cm.