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Knots to Miles per Hour

With the Beaufort force, which is defined in knots.

Inputs
kn

The number of knots to convert.

Miles per hour
23.02mph
In km/h
37.04km/h
In metres per second
10.29m/s
Beaufort force
5 — fresh breeze
10 kn
11.51mph
20 kn
23.02mph
40 kn
46.03mph
100 kn
115.08mph
mph = knots × 1.15078

1 kn = 1.150779 mph

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One knot is 1.15078 miles per hour, or exactly 1.852 km/h. A knot is one nautical mile per hour, and a nautical mile is one minute of latitude — which is why it is used at sea and in the air.

How to use Knots to MPH Converter

  1. Enter the speed in knots. From a forecast, a chart plotter or an aircraft instrument.
  2. Read mph and km/h. With the Beaufort force for wind speeds.

About converting knots to miles per hour

A knot is one nautical mile per hour, and the whole reason it persists in shipping and aviation is the definition of the nautical mile itself: one minute of latitude, fixed by international agreement at exactly 1,852 metres. That relationship makes navigation arithmetic trivial in a way no other unit does. A vessel making 30 knots covers half a degree of latitude in an hour, and a navigator reading a chart marked in degrees and minutes can convert between distance and position without any conversion factor at all. The name is older than the unit. Speed was measured by paying out a line behind the ship with knots tied at fixed intervals and counting how many passed in the time a sandglass ran through — which is also why "knots per hour" is wrong. A knot already contains the per-hour; saying it twice describes acceleration. Wind speed is where most people meet the unit, because the Beaufort scale is specified in knots. It was devised in 1805 to describe what the sea was doing rather than what an instrument read, which is why its bands are uneven and why they have survived the arrival of anemometers — force 8 tells a sailor to expect moderately high waves with breaking crests and spindrift, which is more actionable than 34 to 40 knots. Aviation uses the same unit for the same navigational reason, which is why aircraft airspeed indicators read in knots almost everywhere, including in countries that are otherwise entirely metric.

Frequently asked questions

Why do ships and aircraft use knots?
Because a nautical mile is one minute of latitude, so a speed in knots converts directly into position on a chart. Travelling at 30 knots for two hours covers one degree of latitude — an arithmetic convenience no other unit offers for navigation.
Is a knot exactly 1.852 km/h?
Yes, by definition since 1929, when the international nautical mile was fixed at exactly 1,852 metres. The mph figure of 1.15078 is a derived approximation because the statute mile is defined against the metre separately.
What is the Beaufort scale?
A wind force scale from 0 to 12, defined by observed sea state and specified in knots — force 8 is a gale at 34 to 40 knots. It predates instruments and survives because a description of what the sea is doing is more useful to a sailor than a number.
Is it wrong to say "knots per hour"?
Yes. A knot already means one nautical mile per hour, so "knots per hour" describes acceleration rather than speed. The name comes from the knotted line paid out behind a ship and counted against a sandglass.

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