Knots FAQ

What is a knot as a unit of speed?

A knot is a unit of speed equal to one nautical mile per hour. One nautical mile equals exactly 1,852 meters, or approximately 1.15078 statute miles (the regular miles used on roads in the US and UK).

The knot is used as the standard speed unit in maritime navigation, aviation, and meteorology worldwide. If you hear a wind speed reported on a marine radio or see it in a tropical storm forecast, it will almost certainly be in knots.

Why do sailors and pilots use knots instead of MPH or km/h?

The reason comes down to navigation geometry. The Earth is divided into 360 degrees of latitude and longitude, and each degree is divided into 60 arcminutes. One nautical mile was defined as exactly one arcminute of latitude. This means that if you are navigating by degrees and minutes of latitude on a chart — which sailors and pilots have done for centuries — your speed in knots directly corresponds to your position arithmetic.

For example, if you are traveling at 10 knots and you want to know how many minutes of latitude you will cover in one hour, the answer is simply 10. Using MPH would require a conversion step every time. Knots remove that friction from practical navigation.

Aviation adopted knots from maritime tradition, and the global aviation system standardized on them so that air traffic controllers in any country and pilots flying any aircraft all speak the same speed language.

How fast is 30 knots in MPH?

Thirty knots is a strong speed for a sailboat or moderate for a motorboat. In wind terms, 30 knots falls in the Beaufort Force 7 range — described as a near gale — producing white foam and moderate waves. Most coastal sailors would be reefing their sails at that wind speed.

How fast is 20 knots in MPH?

Twenty knots corresponds to Beaufort Force 5 — a fresh breeze. At sea this produces moderate waves of around 6 feet and whitecaps. For sailboats, 20 knots is an enjoyable sailing wind. Many cruising boats achieve hull speed around this wind range.

How fast is 15 knots in MPH?

Fifteen knots is a moderate breeze — Beaufort Force 4. Most sailors would consider this ideal sailing weather. Small wavelets develop, but conditions remain comfortable for most recreational boaters.

How fast is 50 knots in MPH?

Fifty knots is a full storm — Beaufort Force 10. At 50 knots, seas become very high with overhanging crests, and visibility is reduced by blowing spray. This is not a condition for recreational boating. In aviation terms, 50 knots is the standard crosswind limit for many small general aviation aircraft.

What wind speed in knots makes a hurricane?

According to the Saffir-Simpson Hurricane Wind Scale, a tropical cyclone becomes a hurricane when its maximum sustained winds reach 64 knots (74 MPH / 119 km/h). The categories are:

• Tropical Storm: 34–63 knots (39–73 MPH)
• Category 1 Hurricane: 64–82 knots (74–95 MPH)
• Category 2 Hurricane: 83–95 knots (96–110 MPH)
• Category 3 Hurricane (Major): 96–112 knots (111–129 MPH)
• Category 4 Hurricane: 113–136 knots (130–156 MPH)
• Category 5 Hurricane: 137+ knots (157+ MPH)

The National Hurricane Center always reports storm wind speeds in knots in their official advisories, which is why this converter is useful during hurricane season.

Where does the word "knot" come from?

The term comes from a 17th-century navigational instrument called the chip log. Sailors would throw a wooden float (the chip) overboard attached to a rope with knots tied at regular intervals. As the ship moved forward, the rope paid out; sailors would count how many knots passed through their hands over a fixed time period measured by a sandglass. The number of knots counted gave the ship's speed — in "knots."

The spacing of those knots was calibrated so that one knot per sandglass interval equaled one nautical mile per hour — the same unit we use today.

How fast is a typical sailing yacht in knots?

A typical cruising sailboat has a theoretical hull speed of about 7–8 knots, determined by the waterline length of the hull. Most cruising sailors average 5–6 knots over a passage. Racing sailboats can exceed hull speed significantly through planing; high-performance racing cats and trimarans have exceeded 40–50 knots. The sailing speed record stands above 65 knots.

How fast do commercial aircraft fly in knots?

A commercial jetliner such as a Boeing 737 or Airbus A320 typically cruises at 430–450 knots true airspeed at altitude, which translates to roughly 500–520 MPH ground speed. Larger aircraft like the Boeing 777 cruise closer to 490 knots. The Concorde flew at Mach 2, or about 1,150 knots at altitude.

Is a knot faster than a mile per hour?

Yes — slightly. One knot equals 1.15078 miles per hour. So if something is traveling at 10 knots, it is traveling at 11.51 MPH. When comparing speeds, knots will always be the smaller number: a 100-knot wind is about 115 MPH.