What is a fathom commonly used to measure?

A fathom is primarily used as a unit of depth in nautical contexts, specifically measuring how deep water is. It is equivalent to six feet. Mariners utilize fathoms to assess the depth of water in order to navigate safely and avoid grounding on underwater obstacles.

While the options presented include other measurements, such as weight, length, and volume, fathoms are not used in those capacities. Fathoms specifically relate to depth, making the understanding of this measurement essential for safe navigation at sea.