Fathom

A traditional unit of length equal to six feet (1.83m), used until the early 20th century as the standard British unit for measuring the depth of a mine.

Historical usage

The fathom's origin lies in seafaring rather than mining — from the Old English 'fæthm', the span of a person's outstretched arms — and it remained the standard nautical unit of depth long before and after its adoption underground. British mines used the fathom as their normal unit for shaft depth and level spacing right up until the early 20th century, when it gave way to feet and, eventually, metres.

How it worked

A fathom measured six feet vertically; miners also used it as a unit of area, one fathom square (six feet by six feet, or 36 square feet) in the plane of a vein, for measuring the extent of ground worked or allocated.

Why it was used

As a unit already familiar from everyday seafaring and rough measurement, the fathom gave miners and mine managers a simple, shared way to record and compare shaft depths and level spacing without needing more specialised units.

Regional variation

The fathom was used across the British mining industry generally, not tied to any one region or commodity, though depth figures recorded in fathoms are especially common in older Cornish and Derbyshire mine records.

Sources

1. (secondary) Fathom — Encyclopaedia Britannica
2. (secondary) Fathom: Unit of Depth Equal to Six Feet — UK Sailmakers

Record created: 22 August 2026 · Last researched: 22 August 2026