Convert Fathom to Nautical Mile
Convert fathoms to nautical miles instantly. 1 fathom = 0.000987473 nautical mile — use the live calculator, the exact formula, a conversion table and worked examples. Also check the Nautical Mile to Fathom converter for the reverse conversion.
Units explained
Fathom
A fathom is an Imperial unit of length equal to 6 feet or exactly 1.8288 meters. It is used almost exclusively for measuring water depth in maritime contexts.
The fathom derives from the Old English word fæthm, meaning "the embracing arms" — the distance between the fingertips of a person's outstretched arms. Standardized at 6 feet in English maritime tradition.
Fathoms are used in nautical depth charts, scuba diving, oceanography, and maritime literature. Despite metrication efforts, fathoms remain common in English-language nautical charts and recreational diving.
Old English origin (predating 1066); standardized at 6 feet by English maritime tradition; fixed at 1.8288 m exactly via the 1959 International Yard and Pound Agreement.
Nautical Mile
A nautical mile is a unit of length equal to exactly 1,852 meters, defined as one minute of arc along any meridian of the Earth. It is the standard unit for sea and air navigation worldwide.
Originally defined as one minute of arc along a great circle of the Earth, making it convenient for celestial navigation. The International Hydrographic Organization (IHO) standardized the value at exactly 1,852 meters in 1929.
Nautical miles are used in maritime navigation, aviation, and international law (territorial waters, exclusive economic zones). Speed in nautical miles per hour is called a knot. The nautical mile is distinct from the statute (land) mile.
Defined for celestial navigation since antiquity; standardized to 1,852 m exactly by the IHO in 1929; adopted by the International Civil Aviation Organization (ICAO) for aviation use.
Fathom to Nautical Mile conversion formula
The relationship between fathoms and nautical miles:
To convert fathoms to nautical miles, multiply the value in fathoms by 0.000987473. To reverse, multiply nautical miles by 1012.6859142607.
How to use this converter
Type a value into the calculator. The result in nautical miles updates as you type. Tap a quick value, copy the result with one click, or use the swap arrow to jump straight to the Nautical Mile to Fathom converter for the reverse direction.
Step-by-step: convert fathoms to nautical miles
- Write down the value in fathoms (ftm).
- Multiply that value by the factor 0.000987473.
- The product is the equivalent value in nautical miles (nmi).
- To reverse, multiply the nautical mile value by 1012.6859142607.
Worked examples
Example 1 — Convert 1 ftm to nmi:
1 × 0.000987473 = 0.000987473 nmi
Example 2 — Convert 100 ftm to nmi:
100 × 0.000987473 = 0.0987473002 nmi
Real-world example — Metric distance scale-up
One thousand fathoms equals one nautical mile — the running distance for a 1K race or the standard metric kilometre-scale step. The simple thousand-fold conversion is the most-used metric distance translation.
1000 ftm × 0.000987473 = 0.9874730022 nmi
Real-world example — Imperial mile arithmetic
5,280 fathoms equals exactly one nautical mile. American hikers tracking elevation gain in the smaller unit but trail length in the larger one use this constant every time they read a topographic map.
5280 ftm × 0.000987473 = 5.2138574514 nmi
Real-world example — Imperial yard-to-mile scale
1,760 fathoms equals exactly one nautical mile. American athletes and surveyors use this conversion to translate distances quoted in the smaller imperial unit into recognizable fractions of the larger geographic one.
1760 ftm × 0.000987473 = 1.7379524838 nmi
Fathom to Nautical Mile conversion table
Standard reference values for converting fathoms to nautical miles:
| Fathom [ftm] | Nautical Mile [nmi] |
|---|---|
| 0.01 | 9.87473e-6 |
| 0.1 | 9.87473e-5 |
| 1 | 0.000987473 |
| 2 | 0.001974946 |
| 3 | 0.002962419 |
| 4 | 0.003949892 |
| 5 | 0.004937365 |
| 10 | 0.00987473 |
| 20 | 0.01974946 |
| 30 | 0.0296241901 |
| 40 | 0.0394989201 |
| 50 | 0.0493736501 |
| 100 | 0.0987473002 |
| 500 | 0.4937365011 |
| 1000 | 0.9874730022 |
Frequently asked questions
How many nautical miles is 1 fathom?
How do I convert fathoms to nautical miles?
How do I convert nautical miles back to fathoms?
How many nautical miles is 100 fathoms?
Popular length unit conversions
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Metric / SI (7 units)
Imperial / US Customary (26 units)
Nautical (1 units)
Sources & references
Conversion factor (1 ftm = 0.000987473 nmi) verified against the following authoritative sources:
- BIPM — The International System of Units (SI Brochure 9th ed.)
Official BIPM publication defining the seven SI base units (including the meter) and the rules for their use. The global authority on units of measurement.
- NIST — Guide to the SI
US National Institute of Standards and Technology reference covering the SI base and derived units with definitions and usage rules for US technical practice.
- NIST Special Publication 811 — Guide for the Use of the International System of Units
Detailed NIST guide covering exact conversion factors between SI and US customary units along with formatting and rounding conventions.
- NIST — Refinement of values for the yard and pound (Federal Register 1959)
The treaty (signed by US
- International Hydrographic Organization — Resolution on the Nautical Mile
International authority that standardised the nautical mile at exactly 1852 m in 1929 — the value adopted worldwide for sea and air navigation.