About

In maritime and aviation environments, the Nautical Mile (nmi) is the standard unit of measurement. It is historically based on the circumference of the Earth, specifically approximating one minute of arc of latitude. Unlike the statute mile used on US roads, the nautical mile is directly related to planetary geometry, making it essential for chart work. However, engineering specifications, fuel logistics, and international communication often require metric units (km). Precision is critical here; a rounding error over a long-haul flight path or trans-oceanic voyage results in significant deviations.

This tool adheres strictly to the international standard adopted in 1929, where 1 nautical mile is defined as exactly 1,852 meters. It also includes a calculator for converting degrees of latitude into surface distance, acknowledging the approximation that 1 degree of latitude ≈ 60 nautical miles.

Formulas

The conversion relies on the exact definition set by the International Hydrographic Bureau:

1 nmi = 1.852 km

For latitude calculations, assuming a spherical Earth:

d_km = deg × 60 × 1.852

Reference Data

Distance (nmi)	Distance (km)	Approximate Latitude Arc
1	1.852	1 Minute
10	18.52	10 Minutes
60	111.12	1 Degree
100	185.20	1.67 Degrees
540	1,000.08	9 Degrees
1,000	1,852.00	16.67 Degrees

Frequently Asked Questions

A regular (statute) mile is 5,280 feet (approx 1.609 km). A nautical mile is longer (1.852 km) because it was originally defined as one minute of arc along a meridian of the Earth. This makes it convenient for navigating with charts using degrees and minutes.

Only at the Equator. Lines of longitude converge at the poles, meaning the distance represented by one degree of longitude shrinks as you move north or south. One degree of latitude remains roughly constant everywhere.

The preferred symbols are nmi, NM, or M. The symbol nm is technically the SI symbol for nanometer, though it is often used colloquially for nautical miles in aviation text.