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Convert fathoms to nautical miles

1 ftm=0.0009875nmi

Use the converter below to change any fathoms value into nautical miles instantly — with formula, conversion table, and real-world examples.

0.00098747

Conversion formula

Forward
nautical miles = fathoms × 0.0009875
Reverse
fathoms = nautical miles × 1,012.69

Example: 10 ftm × 0.0009875 = 0.009875 nmi.

About both units

From

Fathom

ftm

The fathom equals exactly 6 feet or 1.8288 meters. It is the traditional marine unit for water depth, used on older nautical charts and in recreational sailing. Modern charts mark depths in metres, but fathoms still appear in maritime literature and older US charts.

Real-world: A "mark twain" reading — made famous by the Mississippi riverboats — meant 2 fathoms (3.66 m) of water, the minimum safe depth.
Read full fathom reference →
To

Nautical Mile

nmi

The nautical mile equals 1852 meters exactly — defined as one minute of arc along a meridian. It is the standard distance unit for marine and air navigation worldwide. Ship and aircraft speeds are given in knots, where 1 knot = 1 nautical mile per hour.

Real-world: Territorial waters extend 12 nautical miles from the coastline. London Heathrow to New York JFK is about 3000 nmi.
Read full nautical mile reference →

Fathom to Nautical Mile conversion table

Common fathoms to nautical miles values for quick reference.

Fathom (ftm)Nautical Mile (nmi)
1 ftm0.0009875 nmi
5 ftm0.004937 nmi
10 ftm0.009875 nmi
25 ftm0.02469 nmi
50 ftm0.04937 nmi
100 ftm0.09875 nmi
250 ftm0.2469 nmi
500 ftm0.4937 nmi
1,000 ftm0.9875 nmi
5,000 ftm4.93737 nmi

Tips & common mistakes

Quick tips

  • 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.

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.

Frequently asked questions

How many nautical miles in a fathom?
One fathom equals 0.0009875 nautical miles.
How do I convert fathoms to nautical miles?
Multiply the fathom value by 0.0009875 to get the equivalent in nautical miles.
What is 100 fathoms in nautical miles?
100 fathoms equals 0.09875 nautical miles.
Is a fathom bigger than a nautical mile?
No. 1 fathom equals 0.0009875 nautical miles, so one fathom is smaller.
How to convert fathoms to nautical miles without a calculator?
Multiply by 0 for a quick estimate; use a calculator for precise results.

Related length conversions

📊 See full comparison matrix →

More from Fathom

ftm → m
1 = 1.8288 m
ftm → km
1 = 0.001829 km
ftm → cm
1 = 182.88 cm
ftm → mm
1 = 1,828.8 mm
ftm → mi
1 = 0.001136 mi
ftm → yd
1 = 2 yd
ftm → ft
1 = 6 ft
ftm → in
1 = 72 in

More to Nautical Mile

m → nmi
1 = 0.00054 nmi
km → nmi
1 = 0.54 nmi
cm → nmi
1 = 5.3996e-6 nmi
mm → nmi
1 = 5.3996e-7 nmi
mi → nmi
1 = 0.869 nmi
yd → nmi
1 = 0.0004937 nmi
ft → nmi
1 = 0.0001646 nmi
in → nmi
1 = 1.3715e-5 nmi

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