What Is a Knot? The Nautical Unit of Speed
Discover the knot — the speed unit used by sailors, pilots, and meteorologists worldwide. Learn its definition, history, conversions, and why it still matters today.
Last updated: 2025-03-15
Introduction: Speed at Sea and in the Sky
A knot (symbol: kn or kt) is a unit of speed equal to one nautical mile per hour. It is the standard speed unit in maritime navigation, aviation, and meteorology. While most of us measure driving speed in miles per hour (mph) or kilometers per hour (km/h), anyone who works on the water or in the air uses knots. Understanding knots is essential for reading marine forecasts, interpreting flight data, or following yacht races and shipping reports.
The Definition and Key Conversions
1 knot = 1 nautical mile per hour = 1.852 km/h = 1.15078 mph
- Knots to mph: mph = knots × 1.15078
- Knots to km/h: km/h = knots × 1.852
- mph to knots: knots = mph × 0.868976
- km/h to knots: knots = km/h × 0.539957
- Knots to m/s: m/s = knots × 0.514444
Worked Examples
Example 1: A sailboat traveling at 8 knots
In mph: 8 × 1.15078 = 9.21 mph. In km/h: 8 × 1.852 = 14.82 km/h. This is a brisk sailing speed in moderate wind.
Example 2: A commercial jet cruising at 480 knots
In mph: 480 × 1.15078 = 552.37 mph. In km/h: 480 × 1.852 = 888.96 km/h. This is a typical cruising speed for a Boeing 737 or Airbus A320.
Example 3: Wind speed of 35 knots
In mph: 35 × 1.15078 = 40.28 mph. In km/h: 35 × 1.852 = 64.82 km/h. On the Beaufort scale, 35 knots is a “near gale” (Force 7), strong enough to make walking difficult.
Quick Reference Table
| Knots | mph | km/h | m/s |
|---|---|---|---|
| 5 | 5.75 | 9.26 | 2.57 |
| 10 | 11.51 | 18.52 | 5.14 |
| 20 | 23.02 | 37.04 | 10.29 |
| 50 | 57.54 | 92.60 | 25.72 |
| 100 | 115.08 | 185.20 | 51.44 |
| 250 | 287.70 | 463.00 | 128.61 |
| 500 | 575.39 | 926.00 | 257.22 |
History of the Knot
The term “knot” dates to the 17th century and the chip log, an early device for measuring a ship's speed. Sailors would toss a wooden panel (the “chip”) attached to a rope overboard. The rope had knots tied at regular intervals — typically every 47 feet 3 inches (14.4 m). As the ship moved forward, the rope would pay out. A sailor would count how many knots passed through his hands in a 30-second sandglass interval. Each knot counted corresponded to one nautical mile per hour. The term stuck, and “knots” became the universal word for nautical speed.
Why Knots Are Still Used Today
Knots persist because of the nautical mile, which is defined as exactly 1,852 meters — one minute of arc of latitude. This makes navigation arithmetic simple: traveling at 30 knots for 2 hours covers 60 nautical miles, which equals exactly one degree of latitude. Charts and instruments are designed around this relationship, and switching to mph or km/h would break centuries of established practice.
Real-World Applications
- Maritime: Ship speeds, current speeds, and wind speeds at sea are all reported in knots.
- Aviation: Airspeed indicators display knots. Air traffic control uses knots for speed instructions.
- Meteorology: Wind speeds in marine and aviation weather forecasts are given in knots.
- Yacht racing: Competitive sailing reports performance in knots. The sailing speed record exceeds 65 knots.
Convert knots to any speed unit using our speed converter.
Frequently Asked Questions
How fast is 1 knot in mph?
One knot equals approximately 1.15078 miles per hour. To convert knots to mph, multiply by 1.15078.
Why do ships and planes use knots instead of mph?
Knots are tied to nautical miles, which correspond to degrees of latitude on Earth. One nautical mile equals one minute of latitude, making navigation calculations much simpler when using knots for speed.
How fast is 1 knot in km/h?
One knot equals exactly 1.852 kilometers per hour. This is because one nautical mile is defined as exactly 1,852 meters.