Knots to miles per hour
Convert knots to mph. Multiply by 1.15078, with hurricane category thresholds and a table of aircraft and marine speeds.
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The formula
mph = knots × 1.1507794480A knot is exactly 1852 metres per hour and a mile is exactly 1609.344 metres, so this factor is that ratio — which does not terminate, hence the rounding.
The useful thing about it is how close it is to 1: a knot is about 15% faster than a mile per hour, and for a rough figure the two can be treated as nearly the same unit in a way km/h and mph cannot.
Quick reference
| Knots | mph |
|---|---|
| 1 kn | 1.15 mph |
| 5 kn | 5.75 mph |
| 10 kn | 11.51 mph |
| 20 kn | 23.02 mph |
| 34 kn | 39.13 mph |
| 50 kn | 57.54 mph |
| 64 kn | 73.65 mph |
| 100 kn | 115.08 mph |
Hurricane categories
This conversion exists mostly because of one thing: American hurricane reporting gives wind in mph while the underlying advisories are issued in knots. The Saffir–Simpson thresholds are defined in knots and the mph figures are the rounded conversions:
| Category | Knots | mph | km/h |
|---|---|---|---|
| Tropical depression | < 34 kn | < 39 mph | < 63 km/h |
| Tropical storm | 34–63 kn | 39–73 mph | 63–118 km/h |
| Category 1 | 64–82 kn | 74–95 mph | 119–153 km/h |
| Category 2 | 83–95 kn | 96–110 mph | 154–177 km/h |
| Category 3 | 96–112 kn | 111–129 mph | 178–208 km/h |
| Category 4 | 113–136 kn | 130–156 mph | 209–251 km/h |
| Category 5 | 137+ kn | 157+ mph | 252+ km/h |
The 74 mph that defines a hurricane is not a round number because the real threshold is 64 knots. Every category boundary in mph is a converted figure.
Aircraft and marine speeds
| Knots | mph | |
|---|---|---|
| Sailing yacht, cruising | 6 kn | 6.9 mph |
| Container ship | 20 kn | 23.0 mph |
| Powerboat | 40 kn | 46.0 mph |
| Light aircraft, cruise | 120 kn | 138.1 mph |
| Airliner, approach | 140 kn | 161.1 mph |
| Airliner, cruise | 480 kn | 552.4 mph |
Estimating in your head
Add 15%. 40 knots plus 6 is 46 mph, which is the exact answer to one decimal place. For a quicker figure still, add a tenth and then a bit — the error from just adding a tenth is under 5%.
See also knots to km/h, where the factor is the far tidier 1.852 exactly.