Convert Knots to mph and kmh and Back - How Fast is a Knot

convert-knots-to-mph-1There are several units used for measuring speed of the boat, wind, water or something else in maritime conditions. In order to avoid confusion and possible dangerous situations, it is vital to know relationship between three most used units: knots, mph and km/h.

Some definitions:

The knot (abbreviated kn) is, by definition, a unit of speed equal to one nautical mile (1.852 km or 1852 m) per hour, or approximately 1.151 mph.

Miles per hour (abbreviated mph) is a customary unit of speed equal to one statute miles (approximately 1609 m) per hour.

Kilometers per hour (abbreviated km/h) is a unit of speed equal to one kilometer (1000 m) per hour.

Feet per second (abbreviated ft/s) is a unit of speed equal to one foot (approximately 0.305 m) per second.

Conversions Between the Most Common Units of Speed

Conversions between the most common units of speed is given in the following table (some values are abbreviated!):

- m/s km/h mph knots ft/s
m/s 1 3.6 2.236 1.944 3.280
km/h 0.277 1 0.621  0.540  0.911
mph 0.447 1.609 1  0.869  1.466
knots 0.514 1.852 1.150 1  1.688
ft/s 0.305 1.097 0.681  0.592 1

In order to convert one unit to another, multiply the first column unit's value with the conversion factor required to calculate the speed in another unit.

Sometimes the speed of the boat is incorrectly expressed as 'knots per hour'. Since knots are nautical miles per hour, 'knots per hour' are 'knots per hour per hour' becoming 'knots per hour squared', which is actually a measure of acceleration and NOT a measure of speed.

How Fast is One Knot

convert-knots-to-mph-2The speed of one knot equals to the speed of 0.514 m/s, 1.852 km/h, 1.150 mph, or 1.688 ft/s.

For example, your boat is traveling at the speed of 10 kn and want to knot how many mph is that.

Speed in mph = speed in knots x conversion factor = 10 kn x 1.150 mph/kn = 11.50 mph

So, a boat traveling at speed of 10 kn is traveling at speed of 11.50 mph, or 5.14 m/s, or 18.52 km/h or 16.88 ft/s.

Fortunately, most modern serious fishing boats measure speed of the boat's hull in the water and real boat's speed with GPS and present it in desired units.

Note: these two speeds can differ significantly in areas with strong sea currents. Be very wary when navigating such waters and pay attention to both values since if you are traveling at the speed of 10 knots through the water up the current and current is 3 knots, your GPS (real speed) is only 7 knots! If you have to travel 20 nautical miles under such conditions, you will need NOT two hours, but almost three hours. Do you have that much fuel on board? And what about wind?

Long story short - it is very easy to remember this conversion table, at least to convert knots to other units. If you want, print it or save it for later.

Electronic devices can be of great aid, but sometimes they are like two edge sword. In order to navigate safely, there is no need to learn how to use sextant and sand watch, but the basics of maritime navigation are required ...