Nautical Miles and Knots

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Nautical Miles and Knots

Nautical miles and knots are often mentioned together, but they measure different things: a nautical mile is a distance, while a knot is a speed. One knot equals one nautical mile per hour. These definitions can be used to calculate distance and time when the speed and period in question are known.

Converting knots to kilometers per hour

One nautical mile equals 1,852 meters, or 1.852 kilometers. Since one knot is one nautical mile per hour, it equals 1.852 kilometers per hour. To convert knots to kilometers per hour, multiply the value by 1.852: 10 knots is 18.52 km/h, 20 knots is 37.04 km/h, and 12 knots is 22.224 km/h. The calculation expresses the same speed in a different unit.

The relationship between distance, speed, and time is: Distance in nautical miles = speed in knots × time in hours. At a constant speed of 10 knots, the distance covered in three hours is 30 nautical miles. The reverse calculation is Time in hours = distance in nautical miles ÷ speed in knots. So a distance of 30 nautical miles at 10 knots also takes three hours. In both formulas, the units must match: knots already include the time element “per hour.”

Distinguishing distance from speed

“12 nautical miles” refers to a distance, whereas “12 knots” means twelve nautical miles per hour. A speed can be converted into distance traveled only once the duration is known. For example, at 12 knots for six hours: 12 × 6 = 72 nautical miles. At 1.852 kilometers per nautical mile, that is 72 × 1.852 = 133.344 kilometers. This sequence shows how speed and time first yield a distance in nautical miles and then a distance in kilometers.

Shorter periods can be used as well. Three quarters of an hour is 0.75 hours. At 8 knots, the calculation is 8 × 0.75 = 6 nautical miles; in kilometers, that is 6 × 1.852 = 11.112 kilometers. To calculate travel time in reverse, divide the distance by the speed. This makes it clear which quantity is being calculated and which values are given.

The examples assume a constant speed over the period used in the calculation. If the speed varies, use a speed value appropriate to the period when calculating time or distance. The formula shows the relationship: distance equals speed multiplied by time.

Nautical miles and knots in a nautical context

Nautical miles are commonly used to indicate distances in navigation and on nautical charts. For depth figures on a chart, the chart datum is also important; the unit of distance alone tells you nothing about it. Knots indicate how many nautical miles are covered per hour. This makes it possible to relate chart distances, speed, and time using the same units.

During a voyage, speed can describe movement through the water or progress over ground. Tidal currents affect the direction and speed of the water and can therefore explain the difference between these two reference frames. Converting between knots and kilometers per hour does not change the reference frame; it simply expresses the speed in a different unit.

A calculation using distance and speed describes the time spent moving along the section of a journey in question. On river and canal routes, depending on the route, locks and possible waiting times must also be taken into account; actual travel time therefore does not necessarily equal the calculated time spent moving.