Knots to mph and km/h: How to Convert Speed

A knot is one nautical mile per hour. Ships, aircraft and weather forecasts use it, while road signs use miles per hour (mph) or kilometers per hour (km/h). Converting between them is a single multiplication once you know where the numbers come from.

The short answer

Knots to mph: multiply by 1.15078. 100 knots is 115.08 mph.
Knots to km/h: multiply by 1.852. 100 knots is 185.20 km/h.
mph to knots: multiply by 0.86898.
mph to km/h: multiply by 1.609344. 60 mph is 96.6 km/h.
km/h to mph: multiply by 0.62137. 100 km/h is 62.1 mph.

The knots to mph converter and the knots to km/h converter give the answer to as many digits as you need.

Why a knot is 1.852 km/h

A nautical mile was originally the distance covered by one minute of latitude, which is why it suits navigation: on a chart, 60 nautical miles is one degree. The Earth isn't a perfect sphere, so that distance varies slightly. In 1929 an international conference fixed the nautical mile at exactly 1,852 meters, and that definition is still used.

So one knot is exactly 1.852 km/h. A statute mile, the one on road signs, is exactly 1,609.344 meters, which makes one knot 1,852 ÷ 1,609.344 = 1.15078 mph. A knot is about 15% faster than a mile per hour.

Knots to mph and km/h table

Knots	mph	km/h
1 kn	1.15	1.85
5 kn	5.75	9.26
10 kn	11.51	18.52
20 kn	23.02	37.04
30 kn	34.52	55.56
50 kn	57.54	92.60
95 kn	109.32	175.94
100 kn	115.08	185.20
150 kn	172.62	277.80
250 kn	287.69	463.00
270 kn	310.71	500.04
500 kn	575.39	926.00

Where you'll see knots

Hurricanes. The U.S. National Hurricane Center rates storms on the Saffir-Simpson scale in knots as well as mph. Category 2 runs from 83 to 95 knots, so a 95-knot storm, about 109 mph, is at the top of Category 2. One more knot makes it a major hurricane.
Aviation. Airspeeds and wind reports are given in knots. In the United States, aircraft below 10,000 feet are generally limited to 250 knots, which is 287.69 mph or 463.00 km/h. 270 knots is about 311 mph.
Boats. A sailboat cruising at 6 knots is moving at about 7 mph. Harbor speed limits are often 5 knots, which is 5.75 mph.
Wind forecasts. Marine and aviation forecasts use knots. Some forecasts, especially in Scandinavia, use meters per second instead: 10 m/s is 36.0 km/h, 22.4 mph or 19.4 knots.

Driving speeds: mph and km/h

mph	km/h
20 mph	32.2
30 mph	48.3
50 mph	80.5
60 mph	96.6
70 mph	112.7
80 mph	128.7

Going the other way, 50 km/h is 31.1 mph, 80 km/h is 49.7 mph, 100 km/h is 62.1 mph and 120 km/h is 74.6 mph. Use the mph to km/h converter or the km/h to mph converter for any other value.

Shortcuts you can do in your head

Knots to mph: add 15%. 100 knots becomes 115 mph; the exact figure is 115.08. For 40 knots, 10% is 4 and 5% is 2, so about 46 mph.
Knots to km/h: double it, then take off 7%. 100 knots doubles to 200, less 14 is 186; the exact figure is 185.2. Doubling alone is close enough for a sense of size.
mph to km/h: multiply by 8 and divide by 5. 50 mph is 400 ÷ 5 = 80 km/h, within about 0.6% of the exact 80.5.
km/h to mph: multiply by 5 and divide by 8. 100 km/h is 500 ÷ 8 = 62.5 mph, against an exact 62.1. Multiplying by 0.6 is quicker but reads about 3.4% low.

Common mistakes

Saying "knots per hour". A knot already means per hour, so "knots per hour" would describe acceleration.
Mixing nautical and statute miles. A nautical mile is about 15% longer. A boat that covers 10 nautical miles has traveled 11.5 statute miles.
Using 1.6 for knots to km/h. That's roughly the factor for miles per hour. For knots it's 1.852, so 100 knots is 185 km/h, not 160.

Related conversions

Every speed unit at once. The speed converter handles knots, mph, km/h, meters per second and feet per second.
Meters per second. Use the m/s to km/h converter for wind speeds and physics problems.
Distances. For miles, kilometers and feet, see the length conversion chart.