9 mm or 9×19mm Parabellum is a firearms cartridge.

9 mm or 9mm may also refer to:

Rail transport modelling

edit
  • N gauge, 1:160 scale, with rails 9 mm apart, representing standard gauge
  • British N gauge, 1:148 scale, with rails 9 mm apart, representing standard gauge
  • H0e/HOn30 gauge, 1:87.1 scale, with rails 9 mm apart, representing narrow gauge
  • OO9, 1:76 scale, with rails 9 mm apart, representing narrow gauge in Britain
  • Gnine/IIp gauge, 1:22.5 scale, with rails 9 mm apart, representing minimum/miniature gauge