The unit of speed at sea, one nautical mile per hour, or 1.852 km/h.
A knot (kn, sometimes kt) is one nautical mile per hour. Since a nautical mile is exactly 1,852 metres, one knot is exactly 1.852 km/h. Because it's already a speed, "knots per hour" is wrong: a boat simply sails at 6 knots.
Conversions
| Knots | km/h | m/s | mph |
|---|---|---|---|
| 1 | 1.852 | 0.514 | 1.151 |
| 5 | 9.26 | 2.57 | 5.75 |
| 10 | 18.52 | 5.14 | 11.51 |
| 20 | 37.04 | 10.29 | 23.02 |
A quick rule: knots × 2 − 10 % ≈ km/h, and knots ÷ 2 ≈ m/s.
Why knots
Speed at sea is tied to distance on the chart: one nautical mile is one minute of latitude, so a boat sailing at 6 knots covers 6 minutes of latitude an hour, easy to measure off the chart. The name comes from the old chip log: a wooden board on a line with knots tied at regular intervals. Sailors threw it over the side and counted how many knots ran out while a sandglass emptied.
Knots are used for boat speed (SOG, STW), wind speed and current, and in aviation too.