Nautical Unit Converter
Convert between knots, km/h, mph, nautical miles, fathoms, and all the other units sailors and mariners need. Type a value and see all unit equivalents instantly. Includes Beaufort scale lookup and passage time calculator. Nothing uploaded.
Beaufort Scale
Passage Planner
Learn more: nautical units and the Beaufort scale
Why a nautical mile is longer than a statute mile
Wikipedia's nautical mile article says the international nautical mile has been defined as exactly 1,852 metres since 1929. It started as the length of one minute of latitude, and it works out to about 6,076 feet, or 1.15078 statute miles.
That ratio is the factor between knots and mph in the tool. A speed of 20 knots is 20 x 1.15078, or 23.0 mph, and 37.04 km/h. A knot is one nautical mile per hour.
Reading the Beaufort scale
The Met Office Beaufort scale guide lists force 0, calm, as under 1 knot, and force 12, hurricane, as 64 knots and over. Force 5, a fresh breeze, is 17 to 21 knots with a moderate sea, and force 8, a gale, is 34 to 40 knots with a very rough to high sea.
The tool uses those wind ranges. Because the scale is written in whole knots, it rounds your speed to the nearest knot before it picks a force, so 21.4 knots is still force 5 and 21.6 is force 6.
Depth and pressure
Wikipedia's fathom article defines a fathom as 6 feet, or 1.8288 m, from the Old English word for outstretched arms. It says fathoms were once the standard depth on English-language charts, that most modern charts use metres, and that US charts still show fathoms and feet. In the tool, 1 metre is 0.546807 fathoms.
Pressure converts between hPa, kPa, bar, psi and inHg. For example, 1013.25 hPa is about 29.92 inHg, which lets you compare a forecast in one unit with a barometer in another.
FAQ
Why is a nautical mile longer than a statute mile?
It began as one minute of latitude, a distance tied to the Earth, and was fixed at exactly 1,852 m in 1929. The statute mile is 1,609 m, so a nautical mile is about 15% longer.
What wind speed is a gale?
Beaufort force 8 is 34 to 40 knots, according to the Met Office guide. The tool shows it as a gale with a high sea state.
Why are fathoms still used?
Wikipedia notes that the US Hydrographic Office still uses fathoms alongside feet on American charts, while most modern charts use metres. One fathom is 1.8288 m, so convert before you compare depths on different charts.