Fathom is a unit used to measure what?

A fathom is a traditional unit of length that is primarily used to measure the depth of water. It has been widely used in nautical and marine navigation for centuries. One fathom is equal to 6 feet or 1.8288 meters. The term is most often used by sailors, divers, and oceanographers when determining how deep the water is beneath a ship or boat.

The word “fathom” comes from the Old English word fæthm, meaning “outstretched arms.” Historically, the term originated from the practice of measuring water depth using a rope or line held between the outstretched arms of a person — the length between fingertips was roughly six feet, which later became standardized as one fathom.

In modern oceanography and marine science, depth is measured using advanced equipment such as echo sounders and sonar systems, but the results are still often expressed in fathoms for tradition and simplicity. For example, sailors might say “the sea is 20 fathoms deep,” which means the water depth is about 120 feet (20 × 6).

Fathoms are also used in fishing, submarine operations, and underwater engineering to describe how deep a particular object or structure is located beneath the surface. Although the metric system is now more common in scientific work, the fathom remains an important nautical unit used internationally in marine navigation charts and depth measurements.

To summarize:

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  1 fathom = 6 feet = 1.83 meters

  
  


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  Used for: Measuring depth of water

  
  


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  Field of use: Marine navigation and oceanography

  
  

Therefore, a fathom is a unit used to measure depth, particularly in oceans and seas.

✅ Correct Answer: B) Depth