Knots to MPH: Why Ships and Planes Use Knots (And How to Convert Any Speed Unit)
If you have ever watched a weather report about a hurricane, followed a flight tracker, or read about a sailing race, you have probably seen speeds measured in "knots." But what exactly is a knot, why do ships and planes use this unit instead of mph or km/h, and how do you convert between them? This guide explains everything you need to know about speed unit conversions.
What Is a Knot?
A knot is one nautical mile per hour. A nautical mile is 1,852 meters (or 1.15078 statute miles, or 6,076 feet). This means:
- 1 knot = 1.15078 mph
- 1 knot = 1.852 km/h
- 1 knot = 0.5144 meters per second
The name comes from a centuries-old method of measuring a ship's speed. Sailors would throw a log attached to a rope overboard. The rope had knots tied at regular intervals, and sailors counted how many knots passed through their hands in a set time period (usually 30 seconds measured by a sandglass). The number of knots that slipped out gave the ship's speed directly - hence "knots."
Why Do Ships and Planes Use Knots?
The nautical mile is not an arbitrary unit. It corresponds to one minute of latitude on the Earth's surface. This relationship makes navigation calculations much simpler. If you are sailing due north and travel 60 nautical miles, you have moved exactly one degree of latitude. This direct connection between distance and the coordinate system of the globe is why maritime and aviation navigation adopted the nautical mile, and by extension, the knot.
Aviation adopted knots from maritime tradition. Aeronautical charts use nautical miles, and air traffic control communicates speeds in knots worldwide. This standardization means a pilot flying from New York to London uses the same speed units as the ship captain crossing below.
Complete Speed Conversion Table
| Knots | MPH | km/h | m/s |
|---|---|---|---|
| 5 | 5.8 | 9.3 | 2.6 |
| 10 | 11.5 | 18.5 | 5.1 |
| 20 | 23.0 | 37.0 | 10.3 |
| 30 | 34.5 | 55.6 | 15.4 |
| 50 | 57.5 | 92.6 | 25.7 |
| 75 | 86.3 | 138.9 | 38.6 |
| 100 | 115.1 | 185.2 | 51.4 |
| 150 | 172.6 | 277.8 | 77.2 |
| 200 | 230.2 | 370.4 | 102.9 |
| 300 | 345.2 | 555.6 | 154.3 |
| 500 | 575.4 | 926.0 | 257.2 |
Real-World Speed References
To put these units in perspective, here are some familiar speeds in all four units:
| Activity / Object | Knots | MPH | km/h |
|---|---|---|---|
| Walking | 2.7 | 3.1 | 5.0 |
| Cycling (casual) | 8.7 | 10.0 | 16.0 |
| City speed limit | 26.1 | 30.0 | 48.3 |
| Highway driving | 60.8 | 70.0 | 112.7 |
| Sailboat (cruising) | 6.0 | 6.9 | 11.1 |
| Container ship | 20.0 | 23.0 | 37.0 |
| Commercial jet | 480.0 | 552.4 | 889.0 |
| Speed of sound | 661.5 | 761.2 | 1,225.0 |
Wind Speed and the Beaufort Scale
Weather forecasts often report wind speed in knots, especially marine forecasts. The Beaufort scale classifies wind strength from 0 (calm) to 12 (hurricane force):
- Force 0 (Calm): less than 1 knot / less than 1 mph
- Force 3 (Gentle breeze): 7-10 knots / 8-12 mph - leaves and twigs move
- Force 6 (Strong breeze): 22-27 knots / 25-31 mph - umbrellas become difficult
- Force 8 (Gale): 34-40 knots / 39-46 mph - twigs break off trees
- Force 10 (Storm): 48-55 knots / 55-63 mph - trees uprooted
- Force 12 (Hurricane): 64+ knots / 74+ mph - widespread destruction
Quick Mental Math for Knots to MPH
If you need a fast estimate without a calculator, multiply knots by 1.15. An even simpler trick: add 15% to the knot value. For example, 20 knots is roughly 20 + 3 = 23 mph (actual: 23.0 mph). For knots to km/h, multiply by 1.85 or nearly double the value minus 10%. For example, 20 knots is roughly 40 - 3 = 37 km/h (actual: 37.0 km/h).
For exact conversions, use our Speed Converter tool, which handles knots, mph, km/h, meters per second, and more.
Frequently Asked Questions
How many mph is 1 knot?
1 knot equals 1.15078 mph. So 10 knots is 11.5 mph, 50 knots is 57.5 mph, and 100 knots is 115.1 mph.
Why don't we just use mph or km/h for everything?
Nautical miles map directly to the Earth's coordinate system (1 nautical mile = 1 minute of latitude). This makes navigation calculations far simpler for pilots and sailors who work with latitude and longitude. Using mph would require constant conversion when plotting courses on charts.
How fast is a knot compared to km/h?
1 knot equals 1.852 km/h. To convert knots to km/h, multiply by 1.852. For a quick estimate, nearly double the knot value and subtract about 8%.
What is the difference between a knot and a nautical mile?
A nautical mile is a unit of distance (1,852 meters or 1.15078 statute miles). A knot is a unit of speed equal to one nautical mile per hour. Saying "knots per hour" is incorrect since knots already means "nautical miles per hour."
How do I convert meters per second to mph?
Multiply meters per second by 2.237 to get mph. For example, 10 m/s equals 22.37 mph. Conversely, divide mph by 2.237 to get m/s.