Wind speed converter
Convert wind speeds between m/s, km/h, mph and knots, and see the force on the Beaufort scale.
Type in any box and the others update as you type.
- Beaufort force
- 5
- 8.0–10.7 m/s
- Description
- Fresh breeze
- On land
- Small trees in leaf start to sway.
- At sea
- Moderate, longer waves with many whitecaps and some spray.
How it works
Converting wind speeds
Every conversion goes through meters per second, the unit most weather services in Europe use. The factors are exact by definition: a kilometer per hour is 1/3.6 m/s, a mile per hour is 0.44704 m/s, and a knot, one nautical mile (1,852 m) per hour, is 1,852/3,600 m/s.
| From | To | Multiply by |
|---|---|---|
| m/s | km/h | 3.6 |
| km/h | m/s | 0.2778 (or divide by 3.6) |
| m/s | mph | 2.2369 |
| mph | m/s | 0.44704 |
| m/s | knots | 1.9438 |
| knots | m/s | 0.5144 |
| knots | km/h | 1.852 |
| km/h | mph | 0.6214 |
Two shortcuts for your head: for m/s to km/h, multiply by 4 and take off 10% (10 m/s → 40 − 4 = 36 km/h). For m/s to knots, double it and take off a little (10 m/s is about 19 knots).
The Beaufort scale
Francis Beaufort, an officer in the British Royal Navy, devised the scale in 1805 so sailors could judge the wind from the sea and their sails. It was later tied to measured wind speeds, and many forecasts, especially for sailing, still give the wind as a Beaufort force.
| Force | Description | m/s | km/h | mph | kn |
|---|---|---|---|---|---|
| 0 | Calm | Below 0.3 | Below 1 | Below 1 | Below 1 |
| 1 | Light air | 0.3–1.5 | 1–5 | 1–3 | 1–3 |
| 2 | Light breeze | 1.6–3.3 | 6–12 | 4–7 | 4–6 |
| 3 | Gentle breeze | 3.4–5.4 | 13–19 | 8–12 | 7–10 |
| 4 | Moderate breeze | 5.5–7.9 | 20–28 | 13–17 | 11–15 |
| 5 | Fresh breeze | 8.0–10.7 | 29–38 | 18–24 | 16–20 |
| 6 | Strong breeze | 10.8–13.8 | 39–49 | 25–30 | 21–26 |
| 7 | Near gale | 13.9–17.1 | 50–61 | 31–38 | 27–33 |
| 8 | Gale | 17.2–20.7 | 62–74 | 39–46 | 34–40 |
| 9 | Strong gale | 20.8–24.4 | 75–88 | 47–54 | 41–47 |
| 10 | Storm | 24.5–28.4 | 89–102 | 55–63 | 48–55 |
| 11 | Violent storm | 28.5–32.6 | 103–117 | 64–73 | 56–63 |
| 12 | Hurricane force | 32.7 or more | 118 or more | 74 or more | 64 or more |
The limits are the World Meteorological Organization's speeds in m/s, converted to whole numbers for the other units. Many tables round each unit on its own, so you may see limits that differ by one, such as 11–16 knots for force 4.
What each force looks like
| Force | On land | At sea |
|---|---|---|
| 0 | Smoke rises straight up. | The sea is flat, like a mirror. |
| 1 | Smoke drifts with the wind, but wind vanes don’t move. | Ripples like scales, without foam crests. |
| 2 | You feel the wind on your face, leaves rustle and wind vanes turn. | Small wavelets with glassy crests that don’t break. |
| 3 | Leaves and small twigs move all the time, and light flags stretch out. | Large wavelets. Crests start to break, with a few whitecaps. |
| 4 | Dust and loose paper lift off the ground, and small branches move. | Small waves, growing longer, with fairly frequent whitecaps. |
| 5 | Small trees in leaf start to sway. | Moderate, longer waves with many whitecaps and some spray. |
| 6 | Large branches move, wires whistle and umbrellas are hard to use. | Large waves start to form, with white foam crests and some spray. |
| 7 | Whole trees move, and walking into the wind takes effort. | The sea heaps up, and foam from breaking waves blows in streaks. |
| 8 | Twigs break off trees, and walking is difficult. | Moderately high, longer waves. Spray blows off the crests in clear streaks of foam. |
| 9 | Light damage to buildings, such as roof tiles and chimney pots blown off. | High waves with dense streaks of foam. Crests topple over, and spray can cut visibility. |
| 10 | Trees are uprooted and buildings badly damaged. Rare inland. | Very high waves with overhanging crests. The sea looks white and visibility is poor. |
| 11 | Widespread damage. Very rare. | Exceptionally high waves, and long white patches of foam cover the sea. |
| 12 | Severe, widespread destruction. | The air is full of foam and spray, the sea is completely white and visibility is very poor. |
Average wind and gusts
Weather services give the wind as an average, measured 10 meters above open ground. The international standard is a 10-minute average, though some countries use a shorter one. Gusts are bursts lasting a few seconds that can be much stronger than the average, so check both before you sail, fly a drone or work at height, and always follow official forecasts and warnings.
More calculators
Other quick calculators
- Percentage calculatorX% of Y, what percent, percentage change, and adding or removing a percentage.
- VAT calculatorAdd or remove VAT at your country's rate, or any rate you choose.
- Discount calculatorSale prices and savings, including stacked discounts.
- Tip calculatorTip and total for any bill, split between people, with rounding up.
- Mortgage calculatorMonthly payment, loan amount and interest from the home price and down payment.
- Loan calculatorMonthly payments, total interest and a full amortization schedule.
- Compound interest calculatorHow savings grow with interest and regular deposits.
- Average calculatorMean, median, mode, range and standard deviation of a list of numbers.
- Age calculatorExact age in years, months and days, and the days until the next birthday.
- Days between datesDays, weeks and weekdays between two dates, or a date plus or minus days.
- BMI calculatorBody mass index in metric or imperial units, with the healthy weight range.
Frequently asked questions
How do I convert m/s to km/h?
Multiply by 3.6. One meter per second is 3,600 meters, or 3.6 kilometers, per hour, so 10 m/s is 36 km/h. To go the other way, divide by 3.6: 50 km/h is about 13.9 m/s.
How strong is a 10 m/s wind?
10 m/s is 36 km/h, 22 mph or about 19 knots. That is force 5 on the Beaufort scale, a fresh breeze: small trees sway and there are lots of whitecaps on open water. Cycling into it is hard work.
How fast is a knot?
One knot is one nautical mile (1,852 meters) per hour: exactly 1.852 km/h, about 0.514 m/s or 1.151 mph. Ships and aircraft use knots because a nautical mile matches one minute of latitude on a chart.
What wind speed is a gale or a storm?
A gale (force 8) starts at 17.2 m/s, which is 62 km/h, 39 mph or 34 knots. A storm (force 10) starts at 24.5 m/s or 89 km/h, and hurricane force (force 12) at 32.7 m/s, 118 km/h or 64 knots.
Why do Beaufort tables give different limits?
The scale is defined in meters per second and knots, and most tables round each of the other units separately, so the limits can move by one between tables. This converter uses the WMO limits in m/s and converts them, so the force it shows always matches the speed you enter.