Units & Conversion · 海里（Nautical Mile） · Updated 2026-10-25
What Is Nautical Mile?
Definition
The nautical mile is the arc length of one minute of latitude, standardized at 1,852 m. Its power is direct chart reading: charts are drawn in latitude-longitude, speed in knots (nmi/hour), so a 120-nmi passage is simply 2 degrees of latitude — no scale conversion. Territorial seas (12 nmi) and EEZs (200 nmi) are legal units too. Historically nations differed (UK 1,853 m, Russia 1,855 m) until 1929 fixed the international 1,852 m.
Formula
1 nmi = 1,852 m; equatorial circumference ≈ 21,639 nmi (360×60)
Worked Example
Shanghai to Busan is ~470 nmi: a cruise ship at 18 kn takes 26 hours; an airliner at 460 kn barely an hour.
Common Misconception
"A nautical mile is 3 li" — a Chinese li is 500 m, so one nmi ≈ 3.7 li. And it is not the statute mile (1,609 m) — a 15% gap. The old character 浬 does mean nautical mile.
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