Nautical unit converter
Convert the units of the sea: wind and boat speed in knots, mph, km/h, m/s and Beaufort force; depths and distances in feet, meters, fathoms and nautical miles; pressure in inches of mercury, hPa and millibars; and temperature in °F and °C.
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- ✓ Printable tables
How to use it
- Type a number in any box: the others in its group update instantly.
- For speed, you also get the Beaufort force and the matching sea state.
- The tables below are printable, to keep on board.
Beaufort scale
| Force | Name | Knots | km/h | m/s | Waves (ft) | Sea state |
|---|---|---|---|---|---|---|
| 0 | Calm | < 1 | < 1 | 0–0.2 | 0 | Sea like a mirror. |
| 1 | Light air | 1–3 | 1–5 | 0.3–1.5 | 0.3 | Ripples without crests. |
| 2 | Light breeze | 4–6 | 6–11 | 1.6–3.3 | 0.7–1.0 | Small wavelets that do not break. |
| 3 | Gentle breeze | 7–10 | 12–19 | 3.4–5.4 | 2.0–3.3 | Crests begin to break; scattered whitecaps. |
| 4 | Moderate breeze | 11–16 | 20–28 | 5.5–7.9 | 3.3–4.9 | Longer waves; frequent whitecaps. |
| 5 | Fresh breeze | 17–21 | 29–38 | 8–10.7 | 6.6–8.2 | Moderate, longer waves; many whitecaps, some spray. |
| 6 | Strong breeze | 22–27 | 39–49 | 10.8–13.8 | 9.8–13 | Large waves form; white foam crests everywhere. |
| 7 | Near gale | 28–33 | 50–61 | 13.9–17.1 | 13–18 | Sea heaps up; foam blown in streaks. |
| 8 | Gale | 34–40 | 62–74 | 17.2–20.7 | 18–25 | Moderately high, long waves; crests break into spindrift. |
| 9 | Strong gale | 41–47 | 75–88 | 20.8–24.4 | 23–33 | High waves; dense foam; visibility reduced. |
| 10 | Storm | 48–55 | 89–102 | 24.5–28.4 | 30–41 | Very high waves; the sea looks white. |
| 11 | Violent storm | 56–63 | 103–117 | 28.5–32.6 | 38–52 | Exceptionally high waves; medium ships hidden in the troughs. |
| 12 | Hurricane force | ≥ 64 | ≥ 118 | ≥ 32.7 | 46 | Air filled with foam and spray; sea completely white. |
The equivalences
- 1 knot
- 1 nautical mile per hour = 1.1508 mph = 1.852 km/h = 0.5144 m/s
- 1 nautical mile
- 1,852 m = 1 minute of latitude = 6,076 ft
- 1 fathom
- 6 ft = 1.8288 m
- 1 foot
- 0.3048 m
- 1 inHg
- 33.864 hPa (millibars) = 25.4 mmHg
- °C
- (°F − 32) × 5/9
- Beaufort
- v ≈ 0.836 × B^(3/2) m/s (WMO formula)
Depths: feet, meters and fathoms
| Meters | Feet | Fathoms |
|---|---|---|
| 1 | 3.3 | 0.5 |
| 2 | 6.6 | 1.1 |
| 5 | 16.4 | 2.7 |
| 10 | 32.8 | 5.5 |
| 15 | 49.2 | 8.2 |
| 20 | 65.6 | 10.9 |
| 30 | 98.4 | 16.4 |
| 50 | 164 | 27.3 |
| 100 | 328.1 | 54.7 |
| 200 | 656.2 | 109.4 |
Pressure: reference values
- 1,040 hPa30.71 inHgStrong high: settled weather.
- 1,013.25 hPa29.92 inHgStandard atmosphere at sea level.
- 1,000 hPa29.53 inHgLow: changeable, windy.
- 980 hPa28.94 inHgDeep low: gale.
- 950 hPa28.05 inHgHurricane or bomb cyclone.
Which units are used where
- At sea, worldwide
- Speed in knots, distances in nautical miles and wind in knots or Beaufort force, by international convention.
- United States
- On land, mph, feet and °F; pressure in inches of mercury. NOAA charts give depths in feet or fathoms and marine forecasts give wind in knots.
- Europe and most of the world
- On land, km/h and meters; pressure in hPa. Marine forecasts often use Beaufort force for wind and meters for waves.
Frequently asked questions
Why are knots used at sea?
Because a nautical mile is one minute of latitude: on a chart you measure distance with the latitude scale on the side. At 10 knots you cover 10 minutes of latitude in an hour.
How many mph is force 7?
Force 7 (near gale) is 28 to 33 knots: 32 to 38 mph, or 50 to 61 km/h. With 13 to 18 ft waves in the open sea.
How many feet in a fathom?
Six. A fathom is 6 ft (1.8288 m) and is still used for depths on some NOAA charts.
Are hPa and millibars the same?
Yes: 1 hPa = 1 mbar. Average sea-level pressure is 1013.25 hPa, which is 29.92 inches of mercury.
What is the difference between a nautical mile and a mile?
A nautical mile is 1,852 m (6,076 ft) and a statute mile is 1,609 m (5,280 ft). One nautical mile is 1.15 statute miles.
More tools
- Tide height at a given timeHow high the water will be at the time you pick, whether it is rising or falling and how long until high tide.
- Tide coefficient calculatorThe tide coefficient for any place and day, or from the tidal range, with the 20–120 scale explained.
- Solunar calendarMajor and minor periods and the activity rating for every day of the month.
- Sunrise and sunsetSunrise, sunset, twilight and golden hour for any place.
All of this, already worked out for your spot
Every coastal town, beach and harbor has its own page with today’s tide, the yearly tide table, sun, moon and the best time to fish.
Where the data comes from
Exact SI equivalences and the World Meteorological Organization (WMO) Beaufort scale.
Spotted a mistake? Tell us · How we calculate tides, sun and moon