Nautical Mile Meridian Distance Calculator

Nautical mile: arc of meridian

A nautical mile (nm) is one minute of arc along a meridian. The international definition (1929, Monaco) fixed it at exactly 1 nm = 1,852 m = 1.852 km. So 1° of latitude = 60 nm anywhere on Earth. Longitude lines crowd together toward the poles, but latitude spacing stays put. To get the meridional distance between two latitudes you use d(nm) = |φ₂ − φ₁| × 60, with φ in decimal degrees. Say you go from 23.55° S to 22.90° S: that's 0.65° × 60 = 39 nm, roughly 72.2 km. The catch is that this only holds along a meridian, on a north-south leg. For tracks heading any other direction, reach for Haversine or the loxodrome.

Applications

Marine GPS navigation, where chart plotters report distances in nm by default. Reading hydrographic charts (DHN in Brazil, NOAA, UKHO). Collision avoidance under COLREG, where CPA and TCPA come in nm. Fishing-zone limits too: a 12 nm territorial sea and a 200 nm EEZ under UNCLOS. And aviation cross-checks, since aeronautical charts run on nm as well.

FAQ

Why is it 1,852 m and not a round number? One minute of meridian arc on the Earth's mean radius works out to about 1,852 m. The 1929 conference took the old geodetic definition and rounded it to that exact figure.

Is the UK nautical mile different? It used to be. The UK Admiralty mile (1,853.184 m) was retired in 1970 when Britain adopted the international nm, though you'll still spot it on old charts.

Does 1° of longitude also equal 60 nm? Only on the equator. Elsewhere a degree of longitude is 60 × cos(φ) nm, and it drops to zero at the poles.