Convert Fathom to Nautical Mile (ftm → nmi)
The fathom is the traditional marine depth unit, equal to six feet, used in nautical charts and diving manuals.
Fathom to Nautical Mile Conversion Table
10 common values| Fathom | Nautical Mile |
|---|---|
| 1 ftm | 0.000987 nmi |
| 5 ftm | 0.004937 nmi |
| 10 ftm | 0.009875 nmi |
| 25 ftm | 0.024687 nmi |
| 50 ftm | 0.049374 nmi |
| 100 ftm | 0.098747 nmi |
| 250 ftm | 0.246868 nmi |
| 500 ftm | 0.493737 nmi |
| 1,000 ftm | 0.987473 nmi |
| 5,000 ftm | 4.937365 nmi |
How to Convert Fathom to Nautical Mile Manually
Step by StepConverting fathoms to nautical miles is straightforward: multiply by the conversion factor. Follow these three steps to do it by hand or in your head.
- 1Take your value in fathomsStart with the number of fathoms (ftm) you want to convert.
- 2Multiply by 0.000987The conversion factor from ftm to nmi is 0.000987. Multiply your value by this number.
- 3Read the result in nautical milesThe result is your value in nautical miles (nmi).
Formula
Multiply the value in fathoms by 0.000987. For the reverse direction, multiply by 1,012.6859.
nmi = ftm × 0.000987ftm = nmi × 1,012.6859Tips
Use these in everyday conversions- 1 fathom = 2 yards = 6 feet = 1.8288 m.
- Modern charts use metres internationally; fathoms are mostly historical.
- The word "fathom" comes from Old English for "outstretched arms" — originally the span of an adult's arms.
Common Mistakes
Avoid these- Reading a modern chart that uses metres as if it were fathoms — a factor-of-1.83 depth error.
- Confusing fathoms with feet on mixed-unit charts.
- Assuming all US charts still use fathoms — NOAA has largely migrated to metres.
About Fathom and Nautical Mile
What is the Fathom?
The fathom equals exactly 1.8288 meters or 6 feet and is the traditional marine depth unit. The word derives from the Old English 'fæðm,' meaning the span of outstretched arms — historically the distance a sailor could measure rope by stretching it from fingertip to fingertip. Used since antiquity for sounding water depth (lowering a weighted line and counting fathom marks), the fathom remains common in nautical charts, diving manuals, and marine literature. Famous from Mark Twain's pen name (a riverboat lead's call meaning 'safe water,' 2 fathoms or 12 feet) and Shakespeare's 'full fathom five,' the unit retains cultural resonance. Modern oceanographic science prefers the meter, but the fathom persists in fishing, recreational diving, and historical maritime contexts. The fathom relates to the foot (1 fathom = 6 ft) and the yard (1 fathom = 2 yd).
- Water depth on older US nautical charts
- Maritime literature and historical navigation
- Sport diving and scuba depth references in the US
A "mark twain" reading — made famous by the Mississippi riverboats — meant 2 fathoms (3.66 m) of water, the minimum safe depth.
What is the Nautical Mile?
The nautical mile equals exactly 1,852 meters and is the international standard distance unit for marine navigation, aviation, and polar geography. It was originally defined as one minute of arc along a meridian — meaning 60 nautical miles equal one degree of latitude. This relationship makes the nautical mile uniquely useful for charts: a navigator can read distance directly off the latitude scale of any map. Adopted internationally in 1929, the nautical mile is used by virtually all maritime nations and in international aviation regulations. The related speed unit is the knot (1 nautical mile per hour). The nautical mile is roughly 1.151 statute miles or 1.852 km. Distinct from the older British nautical mile (6,080 ft) and the US nautical mile (6,080.20 ft), the international nautical mile is now standard worldwide.
- Marine navigation and nautical charts
- Commercial and military aviation distances
- International maritime law (territorial waters = 12 nmi)
Territorial waters extend 12 nautical miles from the coastline. London Heathrow to New York JFK is about 3000 nmi.