This page deals with fathom, a unit of measure. For information about the comic book title and character created by Michael Turner, see Fathom (comics). For information about the celtic rock band see Fathom (band)

A fathom is a unit of measure equal to 2 yards or 6 feet, or 1.8288 metres. The name of the unit derives from the Old English word fæthm meaning 'outstretched arms' which was the original definition of the unit's measure.

The fathom was first used for land measurement but is now restricted to nautical uses, especially the measurement of the depth of water or the length of nautical rope or cable. After metrication, its use for marine navigation was allowed to continue in the UK and Ireland by directives 80/181/EEC and 89/617/EEC, but this authorisation expired on December 31 1999.

It is easy to roughly measure a length of line or rope as a number of fathoms by repeatedly stretching the rope between the two outstretched arms. Water depths have traditionally been measured this way using a weighted line. The word fathom can be used verbally to describe this process.

Analogous units

The fathom is a generic unit and an analogous measure can be found in many cultures. Some are listed below.