What Is a Nautical Mile and Why Are They Used?

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Whether you are new to cruise vacations or a seasoned traveler, picking up on some of the maritime language and terminology is always nice. One term you will likely encounter during your time aboard the ship is “nautical mile.” 

Today, we will explain in detail what a nautical mile is so you can understand the meaning, historical origins, and relevance of the term for cruise vacations. We will also explain how it differs from a land mile. If you are ready to expand your understanding of nautical terminology, let’s jump right in!

What Is a Nautical Mile? 

In simple terms, a nautical mile is a basic unit of measurement based on longitude and latitude coordinates and the circumference of the earth that is used when traveling on the water. More specifically, it measures distances across the surface of bodies of water. Using longitude and latitude is more practical for long-distance travel, which is useful for cruise ships.

In terms of the actual distance covered by the term, a nautical mile refers to exactly one minute of latitude, which is 1/60th of a degree of latitude. As you may know, latitude lines run horizontally across the globe. They provide a reference point when measuring distances from north to south and vice versa. 

There are 360 degrees of latitude surrounding the globe, with each degree being further divided into 60 minutes. This allows for more precise measurements and makes it easier to describe a specific location. 

What Is the Difference Between a Nautical Mile and a Mile on Land? 

While it may sound slightly strange, it differs from a land mile, also known as a statute mile.

As mentioned, a nautical mile is exactly 1/60th of a degree of latitude, which measures 1.15 miles, or 6027 feet, on land. On the other hand, the type of mile you are more familiar with, the statute mile, measures 5280 feet.

1 Mile Marker Sign
1 Mile Marker Sign (Photo Credit: Kent Weakley)

So, aside from the fact that one is used to measuring distance on the water while the other is a unit of measurement for distances on land, nautical miles and statute miles also differ in length. This is because nautical miles are more practical over the water, as they consider the curvature of the planet Earth.

This is less important on land, but it can make a significant difference when accurately measuring distances and describing locations while traveling over the water. 

What Are the Origins of the Term Nautical Mile?

The term is hundreds of years old. In fact, the first recorded use of the term was in a 1637 booklet titled The Sea-Man’s Practice. Centuries ago, sailors would navigate oceans, seas, and other large bodies of water using an astrolabe and nautical charts.

This tool allowed them to measure the angle between the horizon and objects in the sky, like the sun, moon, or constellations of stars, for celestial navigation. This would allow them to determine their latitude and accurately calculate the distance they traveled. 

Vintage Measuring Tools
Vintage Measuring Tools (Photo Credit: Scorpp)

Since this method of calculating and plotting distance considered the curvature of the planet, they needed a new term. The nautical mile is the standard unit of measurement for any sort of long distance voyage over the water. 

Today, nautical miles can be measured much more precisely, but the basic concept behind the term remains, as does the name. 

What Is the Relevance of Nautical Miles for Cruise Ships?

Now that you understand the term, we can explain why this unit of measurement is essential for cruise ship itineraries. 

Since cruise voyages are meticulously planned for safety and efficiency purposes, it is important to plot the route using the most precise unit of measurement. Nautical miles are much more precise when measuring distances on the water. Since a maritime navigation crew needs to be able to calculate routes, estimate travel times, and accurately track the ship’s fuel consumption, the precise nature of the nautical mile is perfect. 

Cruise Ships in the Dominican Republic
Cruise Ships in the Dominican Republic (Photo Credit: Ihor Koptilin / Shutterstock)

Since many cruise vacations involve visiting various ports of call at specific times, the nautical mile helps maritime navigation crews measure arrival times and distances more accurately. If you are interested, you may even find that the itinerary made available to passengers uses the term to describe the journey. 

It is also used for measuring a ship’s speed. Without this unit of measurement, measuring speed in knots would not be possible. 

Beyond being able to show off your understanding of maritime lingo, understanding the concept behind the term will also help you stay more tuned into the ship’s location and the progress of your voyage.


Do all countries use nautical miles for navigation?

The nautical mile is considered the standard unit of measurement internationally, meaning all nations use it to some degree when at sea. While land-based distance measurements tend to vary between the metric and imperial systems, the international nautical mile is used everywhere. 

How would you convert nautical miles to statute miles or kilometers?

If you want a more relatable understanding of the distance a ship has traveled, it is relatively easy to convert nautical miles to your preferred, land-based unit of measurement. While it will not be 100% accurate, a simple calculation will get you pretty close.

To convert nautical miles to statute miles, multiply the number of nautical miles by 1.15078. If you prefer the metric system, you can convert it to kilometers by multiplying the number by 1.852. 

Are nautical miles only used when measuring distance on the water?

No, nautical miles are also used to a certain extent to explain aviation distance. Many airlines, hobby pilots, and air traffic control personnel will use it when measuring distance in the air. This is because the nautical mile offers a more accurate measurement, as it takes the planet Earth’s curvature into consideration. 

With that said, most airline passengers will only see distance measured in miles or kilometers, as it would be somewhat confusing to display nautical miles. 

Final Words

The nautical mile plays a vital role in navigation at sea. For cruise ships, it helps the crew maintain safe and precise itineraries. This tried and tested unit of measurement has been around for centuries, and it still continues to prove its worth to the present day.

Read Also: Decoding Distance – Statute Miles vs Nautical Miles

The next time you are relaxing on a cruise ship, make sure that you take some time to take in the view of the open water. Knowing that even the planet’s curvature needs to be considered when planning your voyage will help you appreciate the vastness of the ocean or sea you are traversing. It will also help you appreciate the skill and effort that goes into keeping you safe and satisfied on the water!

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