About

In maritime and air navigation, the Statute Mile is rarely used. Instead, the Nautical Mile (NM) is the standard, historically defined as one minute of latitude along any meridian. Precision in converting these units is critical for charting, fuel estimation, and safety protocols.

This comprehensive tool serves two distinct purposes: it acts as a bi-directional converter for navigational units and provides a "Distance to Horizon" calculator. The latter is vital for visual lookouts, determining the range at which a lighthouse or another vessel becomes visible based on observer height.

Formulas

The distance to the horizon (d) in nautical miles depends on the height of the eye (h) in feet. The standard approximation includes terrestrial refraction:

d (NM) ≈ 1.17 × √h (ft)

For metric calculations (d in km, h in meters):

d (km) ≈ 3.57 × √h (m)

The Speed/Time/Distance triangle follows standard kinematics:

Distance = Speed (knots) × Time (hours)

Reference Data

Unit	Symbol	Definition	Metric Equivalent
Nautical Mile	NM	1 minute of Latitude	1.852 km
Knot	kt	1 NM per hour	1.852 km/h
Statute Mile	mi	5,280 feet	1.609 km
Cable Length	cb	1/10th of a NM	185.2 m

Frequently Asked Questions

A Nautical Mile is based on the Earth's geometry (1 minute of arc of latitude), making it useful for map navigation. A Statute Mile (regular mile) is an arbitrary length of 5,280 feet established by Queen Elizabeth I.

It is an approximation that assumes standard atmospheric refraction. In specific weather conditions (like temperature inversion), light can bend more, allowing you to see further than the calculated distance.