Fathom (ftm)

NauticalTraditional unit (still used in some regions)

6 feet (1.8288 m), traditionally the span of a man's outstretched arms. Still used for water depth on nautical charts in some countries.

1 fathom = 1.8288 meters (exactly).

About the fathom

Old English fæðm meant a pair of outstretched arms, and the word gave English its fathom. That is the origin of the measure: the span between the fingertips of a man with his arms spread wide, roughly the height of a person. Because bodies differ, the fathom was not fixed for centuries. Merchant ships are recorded as using about five and a half feet, and fishing boats five or seven, until the length was settled at six feet in the nineteenth century.

Sailors counted in fathoms because a hand sounding line carried marks at fathom intervals, so the depth could be read off when the weight touched bottom. Water shallower than 100 fathoms was said to be in soundings. Anchor chain and fishing line were also sold and counted in fathoms. The figure used here is exactly six feet, or 1.8288 m, which makes two yards one fathom. Most charts today show metres, though some national charts still print fathoms.

Sources: Wikipedia: Fathom; NIST SP 811, Appendix B.8 (length conversion factors)

Fathom conversion chart

1 fathom expressed in every other length unit:

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