A fathom is a unit of length in the US customary and imperial systems of measurement equal to 6 feet or 1.8288 meters.

What is a fathom

A fathom is a measurement of length that is specifically used to measure the depth of water in the US customary and imperial systems of measurement. Because the fathom is neither an SI (International System of Units) unit nor one that is accepted for use within SI, it is a rarely used unit of measurement. It is only used in nautical contexts in the United States due to tradition. Most other countries around the world use meters to measure water depth instead.

Fathom definition

The fathom today is defined as 6 feet or 1.8288 meters. Its original definition however, was based on the distance between the tip of the middle finger of one hand to that of the other hand when both arms are fully stretched out. Since only sailors typically used fathoms to measure water depth, the definition of the fathom was generally based on the arm span of the average sailor of the time, which was approximately 6 feet.

Also, the fathom used to be defined based on the US survey foot rather than the international foot, though this definition is only slightly different. Based on the US survey foot, the fathom is equal to 1.828804 meters rather than 1.8288 meters using the international foot.

Fathom meaning

The term "fathom" was derived from the Old English term "fæðm" which means "a pair of outstretched arms." The definition of a fathom equalling approximately 6 feet was based on the average arm span of sailors of the time, since only sailors or those with maritime occupations had a need to measure water depth.

How deep is a fathom

A fathom is 6 feet or 1.8288 meters deep. Below are other common measures of length and their relationship to a fathom.

Fathom usage

Historically, the fathom was the most widely used measure of water depth. It was also used to measure the depth of mines in the UK up until the 20th century and for burials at sea, which required a minimum depth of 6 fathoms.

Since the widespread adoption of SI, the fathom has been replaced by the meter for measurements of water depth in most countries (with the exception of countries such as the US).

How to convert fathoms

Since most other countries around the world use other units of measurement, it can be helpful to know how to convert fathoms to other units of length. To convert between fathoms and other measurements, we need to know the appropriate conversion factors.

Fathoms to feet

To convert fathoms to feet, multiply a value in fathoms by 6.

Fathoms to meters

To convert fathoms to meters, multiply a value in fathoms by 1.8288.

Fathoms to yards

To convert fathoms to yards, multiply a value in fathoms by 2.

Fathoms to inches

To convert fathoms to inches, multiply a value in fathoms by 72. Below are some fathom conversion examples.


Convert the following measurements between fathoms, meters, and feet.

1. 12 fathoms:

12 × 1.8288 = 21.9456

12 fathoms × 6 = 72 feet

2. 43 meters:

43 ÷ 1.828804 = 23.513 fathoms

43 × 3.28084 = 141.076 feet

3. 215 feet:

215 ÷ 6 = 35.833 fathoms

215 × 0.3048 = 65.532 meters

Fathom conversion table

The table below converts fathoms to common measures of feet and meters.

Fathoms Feet Meters
0.01 0.06 0.018288
0.1 0.6 0.18288
1 6 1.8288
2 12 3.6576
3 18 5.4864
5 30 9.144
10 60 18.288
20 120 36.576
50 300 91.44
100 600 182.88
1000 6000 1828.8

Did you know?

Samuel Langhorne Clemens was one of the most famous Americans of the 1800s. The author of several books, including The Adventures of Tom Sawyer, he is best remembered by his pen name, Mark Twain. This name may have come from his work as a steamboat pilot. To steer the steamboat, the water needed to be 2 fathoms deep, or "by the mark, twain" to be in safe water.