Measure Distance In Water: 9 Facts(Read This First!)

Distances can be measured in the air, on land, and in water. Just like with land and air, measuring distance in water offers advantages of its own. So, let us quickly analyze what prompted the need to measure distance in water.

“Water distance” refers to the distance measured through the water rather than ground or air. In aviation, air distance is crucial. Similarly, knowing the distance traveled by the vessel is essential when navigating across water. Water distance, like air distance, is measured in nautical miles.

Considering the significance of measuring water distance, let us focus on how and when distance is measured in water, as well as many other aspects of measuring distance in water in depth in this article.

When is the distance measured in water?

At all times, measuring distance is not physically possible. Let us now look at the various scenarios in which measuring the distance across the water is necessary.

Water distance is useful for swimmers, sailors, and, of course, every country’s naval force to keep their country’s water border safe. Additionally, the maritime boundaries of countries whose borders are oceanic are determined by measuring water distance, which is commonly 12 nautical miles.

Why is distance on water measured in nautical miles?

Distances in water and air are measured in nautical miles. Miles or kilometers are typically not used to measure distances in water. So, let us look at why we favor nautical miles in water and air over miles and km.

Nautical mile definition en 1
Image Credits: Wikimedia

The nautical mile, a unit of distance, is based on the earth’s circumference and is equal to one minute of latitude. Because the earth is circular, the nautical mile allows for the earth’s curvature as the distance traveled in one minute. Due to its accuracy, it is used in navigation and mapping.

What does knot mean when it comes to navigation?

Different units show every quantity. So let us see what the knot denotes in the navigation.

The knot is a conventional unit to denote the speed of the vessel in nautical miles per hour. The symbol used to denote a knot is kn.

How is distance measured in water?

Many ancient techniques were used to guide sailors at the beginning of ocean navigation. But today, precise devices are widely available. Let us have a look at how they are assisting us:

  • The Speed and Log Device: This marine equipment keeps track of the vassal’s speed in knots and the distance it travels.
  • Global Positioning System (GPS) Receiver: It displays the ship’s current location. It will be simpler for you to measure your progress if you are aware of your starting point.

How do you track distance in open water swimming?

Measuring the distance becomes slightly more difficult if you are swimming in open water. So let us talk about how to track your distance while swimming in open water. 

With today’s smart watches, which include the feature of tracking swimming distance as well, it is simple for you to keep track of your swimming distance. If not, you can store your phone in a dry pouch for GPS tracking or calculate your swimming distance by knowing your strokes per minute.

How do you measure the distance of a river?

Considering that rivers are not straight, they have curves. So, let us look at how to determine the length of any river.

A river’s length can be determined using the twine method. A twine is placed along the feature to be measured from one end to the other, carefully following all curves and bends. The twine is then measured in the appropriate unit of length.

Problem: What distance can a boat travel in 3 hours at a speed of 5.5 knots?


Time taken by the boat to travel the distance T = 3 hours = 120 minutes

Speed of the boat S = 5.5 knots

To Find:

Distance covered by the boat D = ?


We know that

Speed (s) = Distance (D) / Time (T)

Since we are measuring time in minutes, the distance traveled by boat is calculated as follows:

Distance (D) = [Time (T) × Speed (S)] / 60

∴ Distance (D) = [120 × 5.5] / 60 =11 nautical miles

As a result, the boat covers 11 nautical miles in 3 hours at a speed of 5.5 knots.

Note: There is no need to divide the equation by 60 if you consider the trip period in hours.


We learn from this article that measuring a distance across water differs from measuring a distance across a road. Furthermore, the nautical mile measurement is employed to measure sea distance because it is based on the earth’s circular circumference.

Read about Measure Distance In Air.

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