To cite package units in publications use:

Edzer Pebesma, Thomas Mailund and James Hiebert, 2016. Measurement Units in R. The R Journal, 8 (2), 486--494

Corresponding BibTeX entry:

  @Article{,
    author = {Edzer Pebesma and Thomas Mailund and James Hiebert},
    title = {Measurement Units in {R}},
    journal = {The R Journal},
    year = {2016},
    volume = {8},
    number = {2},
    pages = {486--494},
    month = {december},
    url = {https://journal.r-project.org/archive/2016/RJ-2016-061/},
  }