British/American nautical measure adds a number of units to the United States customary and the British Imperial units of length or distance. Prior to 1959, the units had been slightly different in the two countries: British Imperial nautical measure was based on the British Imperial Yard, and United States nautical measure was based on the United States customary yard. With the 1959 agreement unifying the two systems, both were made equal to the International yard.

The units in the British/American nautical measure that are additional to the United States customary and British Imperial systems are listed in the table below.

Name of unit Value in terms of smaller units Value in terms of the meter Value in terms of United States customary measure
fathom 2 yards 1.8288 2 yd = 0.0011 mi
UK nautical chain 2½ fathoms 4.572 5 yd = 0.0028 mi
cable length 408/15 UK nautical chains = 101⅓ fathoms 185.3184 202.6667 yd = 0.1152 mi
nautical mile 10 cable length 1853.184 1.1515 mi
nautical league 3 nautical miles 5559.552 3.4545 mi

It should be noted that the nautical chain was only used in the United Kingdom, and the cable length and nautical league are essentially obsolete.