Kilometer
A kilometer (or km) was a metric unit of length equal to 1,000 meters. 

This unit of measure was used or understood by several species and organizations including the Klingons (who also use the comparable kellicam), the Humans, the Bajorans, the Cardassians, the Tanugans, Ja'Dar's species, the J'naii, the Yridians, the Takarans, the Iyaarans, the Nezu, the Entharans, the Devore, Yost's species, the Varro, the Eska, the Vulcans, the Tellarites, the Oran'taku, the Andorians, the Xindi, and within the Federation.

Comparative units of length 
 In June of 2151, Lieutenant Malcolm Reed detected a ship less than 1 kilometer away from  on the surface of the planet housing the Vulcan monastery at P'Jem. ()
 The Novans dug 12.6 kilometers of tunnels beneath the surface of Terra Nova. ()
 The  closed up on a Nausicaan ship from a 100 kilometers to 9 kilometers until they had locked their plasma cannon on this ship. When  arrived at the scene and dropped out of warp they were 200.000 kilometers away. ()
 The impact crater of the asteroid who hit Terra Nova was 500 kilometers north of the Terra Nova colony. ()
 At the distance of 200.000 kilometers, Enterprise had a first view on the planet Terra Nova, displayed on the viewscreen. ()

External link 
 
Measurements