Knots and Nautical Miles

[Please note first] This app does not measure your speed or your position. It only converts units. It shows no weather or storm information, and it is not a substitute for a nautical chart. Mach and the Beaufort scale are not included: the speed of sound changes with temperature, and a Beaufort force is a range rather than a single speed. ────────── ⇄ Knots and Nautical Miles — sea units in land terms English calls both of them a mile, but a land mile is 1,609.344 m and a nautical mile is 1,852 m. They differ by about 15 percent, and mixing the two up is the commonest mistake in this subject. Convert knots, nautical miles and cables into km/h, m/s, mph, km, m and land miles. ■ Two tabs ▪ Speed — knots, km/h, m/s and mph ▪ Distance — nautical miles, km, m, land miles and cables Tap a unit on either row to convert in that direction. ■ 1,852 m was decided, not discovered In 1929 the First International Extraordinary Hydrographic Conference, held in Monaco, fixed the international nautical mile at 1,852 m. Because it is a defined figure, the word "about" never belongs in front of it. That is also why 200 nautical miles comes to exactly 370.4 km, the outer limit of an exclusive economic zone, counted from the baseline. ■ Three lengths once shared the name Alongside the international 1,852 m there was an Admiralty mile of 1,853.184 m (exactly 6,080 international feet, dropped in 1970) and a US nautical mile of about 1,853.2487 m (6,080.20 survey feet, a rounded figure, replaced by the international one in 1954). Over 100 nautical miles that is a gap of 118.4 m and about 124.9 m. None of them is in use today, so they are not offered as units. They are in the notes instead. ■ It began as a minute of latitude, and that part was never exact A real minute of latitude runs from about 1,843 m at the equator to about 1,862 m at the poles, because the Earth is not a perfect sphere. The figure of 1,852 m was picked from the middle of that spread and then fixed. What is exact is the nautical mile itself, not the Earth. ■ Quick tables ▪ Speed — 1, 5, 10, 15, 20, 25, 30 and 50 knots in km/h, m/s and mph ▪ Distance — 1, 5, 10, 20, 50, 100, 200 and 500 nautical miles in km, mi and cb ■ Unit notes ▪ knot — one nautical mile per hour ▪ m/s — how Japan states the strength of the wind ▪ mph — road speeds in the US and UK, not a sea unit ▪ NM — exactly 1,852 m ▪ mi — exactly 1,609.344 m, the land mile ▪ cb — one tenth of a nautical mile, exactly 185.2 m ■ Good for ▪ Making sense of a figure in knots from the news ▪ Reading a speed given in mph ▪ Getting a feel for how far 200 nautical miles is ▪ Checking whether a mile is the land one or the sea one ■ Things worth knowing (included in the app) ▪ A knot is a knot: knots on a line were counted as it ran out astern ▪ One knot is exactly 1.852 km/h, because the nautical mile is exact ▪ A land mile and a nautical mile differ by about 15 percent ▪ The 1,852 m figure was fixed in 1929 ▪ Three different lengths once went by the name nautical mile ▪ It began as a minute of latitude, and that part was never exact ■ How the app is built ▪ A single screen. No settings page ▪ Your last five entries are kept and can be tapped to restore ▪ The result copies with one tap ▪ Japanese and English, following your device language ▪ No account needed. Every conversion runs on your device and the figures you type are never sent anywhere ────────── Note: this app cannot measure your speed or your position, shows no weather information, and is not a substitute for a nautical chart. Mach and the Beaufort scale are out of scope. The Admiralty and US nautical miles are not offered as units, because neither is in use.