The Ultimate Guide to Understanding Knot Speed

The open ocean can be a difficult place to navigate. For pilots and captains, while the land offers several somewhat permanent fixed visible cues for landmarks, the sea rarely has such distinguishing features. It is because of this complexity that marine navigation has evolved to include such units of measurement as the knot and nautical mile.

What Is Knot Speed?

One knot is equal to 1.15 miles per hour or 1.85 kilometers per hour and one nautical mile is equal to 1.15 miles or 1.85 kilometers.

The term “knot,” in reference to measuring the speed of air and water currents as well as boats and aircrafts, is defined as one nautical mile per hour. A nautical mile is slightly more than a standard mile.

Visualizing Knot Speed

A chart can be found below to visually compare knots to miles per hour for better understanding.

Origins of the Knot

The term “knot” originated in the 17th century when sailors determined their speed through the water by using a device called a “chip log.”  This device is a coil of rope with knots tied in it at specific increments, with a pie-shaped piece of wood attached to the end.  To use it, the piece of wood was dropped off the stern of a ship and dragged behind the moving vessel. The rope was then spooled out freely as the piece of wood fell behind the ship for a specific amount of time.  However many knots were dragged behind the boat by the piece of wood determined the speed of the ship, and the term “knot speed” was born.

Today, knots are still used in both maritime activities and aviation.  While there have been different definitions of a nautical mile throughout history and in different regions, there is an international nautical mile that is used to measure knots today.

What Is a Nautical Mile Compared to a Mile?

1 nautical mile equals 1.15 miles. The nautical mile is based upon the circumference of the Earth. If the equator was a circle, imagine it divided into 360 degrees like a compass. Now split each of those 360 degrees into 60 equal parts called “minutes.” The length of each “minute” along the circumference of the Earth is equal to approximately one nautical mile.

• For example:
  • 1 Knot = 1 Nautical Mile Per Hour = 6076 Feet Per Hour
  • This is because the international nautical mile is defined at 6,076 feet. Therefore, 1 Knot is the same as covering the distance of 6,076 ft/hr.

The length of a nautical mile is closely tied to the longitude and latitude of the Earth’s geographic coordinate system. Therefore, the knot and nautical mile are the units of choice in the marine and aviation industries.

Nautical Mile Conversion

How to Convert Knots to Miles Per Hour (MPH) and Kilometers Per Hour (KPH)

Converting knots to miles per hour or kilometers per hour is straightforward once you know the conversion rates:

• 1 knot = 1.15 miles per hour (MPH)
• 1 knot = 1.85 kilometers per hour (KPH)

Here’s a simple chart to convert different speeds:

Knot Speed in Aviation and Maritime Use

Knots are not just reserved for use on the water—they are also used in aviation to measure wind speed and aircraft velocity. Both industries rely on knots because their navigational charts are based on the Earth’s geographic coordinate system. Whether you’re at sea or in the air, knowing how to measure and understand knots can be crucial.

• Maritime Use: Ships use knots to determine the speed and distance traveled across the ocean. Navigation charts, GPS systems, and even autopilot systems use knots as the standard unit of speed.
• Aviation Use: In aviation, airspeed is measured in knots. Pilots use this unit of speed to calculate their ground speed, which is crucial for determining flight time and fuel consumption.

The Importance of Knot Speed in Weather Forecasting

Knot speed is an integral part of weather forecasting, especially when dealing with marine conditions or aviation. Meteorologists often use knots to report wind speeds and ocean currents, helping sailors and pilots prepare for changing weather patterns.

Visualizing Wind Speed Categories

Why Is Speed Measured in Knots Instead of Miles Per Hour?

Knots are often used in place of miles per hour (MPH) for windspeed as the measurement of wind intensity originated in a nautical context. Sailors have not always had GPS navigation. The nautical mile was introduced in the 15th century, equal to 1.852 kilometers or 6,076 feet, as a standard against which to measure distance. The development of the nautical mile also led to the world’s first speedometer, the chip log. Over time, the chip log was standardized such that the chip was a quarter circle with either a five- or six-inch radius, and lead was added to the bottom of the chip to ensure that it submerged and oriented correctly to provide a more accurate and repeatable reading.

Knots and nautical miles are still used in today’s pilothouses and cockpits because maps used at sea and in the air are based on the Earth’s circumference. 

Final Thoughts

Understanding knot speed and its relationship to nautical miles and MPH is essential for anyone navigating the open ocean or the skies. Whether you’re a sailor, pilot, or weather enthusiast, learning about knots gives you the advantage of accurate navigation and forecasting. For those looking to get precise wind speed readings at home, Maximum Weather Instruments offers a range of wind speed instruments like the Merlin and Maestro to help you stay prepared.