Units
How to Convert Knots to mph (and km/h) — Quick Guide
Published · Last checked October 2026
To convert knots to miles per hour, multiply by 1.15. To convert knots to kilometres per hour, multiply by 1.852. So 10 knots is about 11.5 mph or 18.5 km/h. Going the other way, divide mph by 1.15 to get knots. A knot is one nautical mile per hour, and a nautical mile (1,852 m) is longer than a land mile, which is why the number in knots is smaller.
The conversion factors
| From | To | Multiply by |
|---|---|---|
| Knots | mph | 1.151 |
| Knots | km/h | 1.852 |
| Knots | m/s | 0.514 |
| mph | Knots | 0.869 |
| km/h | Knots | 0.540 |
Quick reference table
| Knots | mph | km/h |
|---|---|---|
| 5 | 6 | 9 |
| 10 | 12 | 19 |
| 15 | 17 | 28 |
| 20 | 23 | 37 |
| 25 | 29 | 46 |
| 30 | 35 | 56 |
| 40 | 46 | 74 |
| 50 | 58 | 93 |
Mental shortcuts
- Knots to mph: add 15%. 20 knots plus 3 gives 23 mph.
- Knots to km/h: double it and take off 10%. 20 knots doubled is 40, less 4 is 36 (exact: 37).
- Knots to m/s: halve it. 20 knots is about 10 m/s.
Why sailors use knots
A knot is one nautical mile per hour, and a nautical mile is a minute of latitude. That makes speed, time and chart distance work together without conversion: at 5 knots you cover 5 miles of the chart's latitude scale in an hour. The name comes from the old log line, a rope with knots at regular intervals paid out astern while a sandglass ran; the number of knots that ran out gave the speed.
Wind speeds in UK marine forecasts are given in Beaufort forces or knots. Learn to read them in the weather awareness lesson.