What This Converter Does
Pick a wind speed and its unit and get the same wind expressed five ways at once: mph, km/h, knots, m/s, and its Beaufort force number with a plain-language description. The units are all interchangeable through fixed factors — 1 knot = 1.15078 mph = 1.852 km/h = 0.514 m/s — so nothing is estimated except where a speed falls on the 0–12 Beaufort scale, which is a range by design. It's built for the moment a forecast, a chart, or a spec sheet hands you the wrong unit.
A Worked Conversion
Say a sailing forecast reports 20 knots. Multiply by 1.15078 for 23 mph, by 1.852 for 37 km/h, and by 0.514 for 10.3 m/s. That speed sits at Beaufort 5, a 'fresh breeze' — whitecaps forming across the water, spray, and moderate waves 4 to 8 feet. Step it up to 34 knots (39 mph, 63 km/h) and you cross into Beaufort 8, a gale: twigs break off trees and it's hard to walk into the wind. The jump from a fun day out to a reef-the-sails day is only 14 knots.
Why the Units Differ
Mariners and pilots use knots because one nautical mile equals one minute of latitude, so speed in knots reads straight off a chart. Metric weather services report km/h or m/s; American forecasts and road signs use mph. The Beaufort scale, devised by Royal Navy officer Francis Beaufort in 1805, skips numbers entirely and describes what the wind is doing to the sea and land — which is often what you actually want to know before heading out.
Wind Speed Converter
How to Use This Calculator
- Enter the Wind Speed: Type the number from your forecast or instrument — for example 18 from an 18-knot marine report.
- Choose the Unit It Came In: Select mph, km/h, knots, m/s, or Beaufort so the tool knows how to read your number. Pick knots for a marine or aviation report, m/s for a metric drone spec.
- Click Calculate: The converter scales your value to every other unit and finds its Beaufort force. Results appear instantly, computed in your browser.
- Read Across the Units: Compare mph, km/h, knots, and m/s side by side, then use the Beaufort force and description to judge the actual conditions.
How It Works
Every unit here measures the same thing — distance covered per unit of time — so conversion is just multiplying by a fixed factor. The one anchor to remember is the knot: 1 knot = 1.15078 mph = 1.852 km/h = 0.514 m/s. Beaufort is different: it's a 0–12 force scale, not a linear unit, so the converter snaps your speed into the nearest force band.
The basic rule:
- 1 knot = 1.15078 mph = 1.852 km/h = 0.514 m/s
- 1 mph = 0.868976 knots = 1.60934 km/h = 0.44704 m/s
- 1 m/s = 1.94384 knots = 2.23694 mph = 3.6 km/h
- Beaufort 0 = calm (under 1 mph), 5 = fresh breeze (19–24 mph), 8 = gale (39–46 mph), 12 = hurricane force (73+ mph)
Wind rarely holds one value — a 20-knot average can gust to 30. Treat any single conversion as the steady wind, and check gust figures separately before you sail, fly, or launch a drone.
Tips & Considerations
- A forecast usually gives a sustained wind and a gust — convert both, since a 20-knot average gusting to 30 knots is a different day than a steady 20.
- Beaufort 5 (fresh breeze, 19–24 mph) is the rough line where whitecaps cover open water — a handy visual check that your conversion is right.
- Most consumer drones top out around Beaufort 5 (about 10 m/s or 22 mph); treat anything above that as a no-fly forecast.
- To go from km/h to mph fast in your head, multiply by 0.6 — 40 km/h is roughly 24 mph, close to the exact 24.9.
- Hurricane force starts at 74 mph (64 knots, Beaufort 12); tropical-storm warnings begin near 39 mph (34 knots, Beaufort 8).
Frequently Asked Questions
How do you convert knots to mph?
Multiply knots by 1.15078. So 20 knots = 23.0 mph, and 35 knots = 40.3 mph. A knot is one nautical mile per hour, and a nautical mile (6,076 ft) is longer than a statute mile (5,280 ft), which is why the mph number is always the bigger one.
Why do sailors and pilots use knots instead of mph?
One nautical mile equals one minute of latitude, so on a chart a speed in knots translates directly into distance along a meridian. That makes dead-reckoning navigation simple: at 6 knots you cover 6 nautical miles, or 6 minutes of latitude, each hour. Marine and aviation forecasts stick to knots for the same reason.
How do I read the Beaufort scale?
It's a 0–12 scale describing what the wind is doing, not a precise number. Force 0 is glassy calm; Force 3 (8–12 mph) is a gentle breeze that raises small flags; Force 5 (19–24 mph) is a fresh breeze with whitecaps everywhere; Force 8 (39–46 mph) is a gale that breaks twigs off trees; Force 12 (73+ mph) is hurricane force. Worked example: 20 knots = 23 mph = 37 km/h, which lands at Beaufort 5, a fresh breeze with moderate waves and spray.
How do I convert m/s to mph?
Multiply meters per second by 2.23694. So 10 m/s = 22.4 mph and 15 m/s = 33.6 mph. Metric weather services (and most drone spec sheets) quote wind in m/s, so a drone rated for 10 m/s can handle roughly 22 mph before it struggles to hold position.
What wind speed is dangerous?
By Beaufort: at Force 6 (25–31 mph) umbrellas turn inside out and walking gets hard. Force 8 gale (39–46 mph) snaps small branches. Force 10 storm (55–63 mph) uproots trees and damages roofs. At 74+ mph you are in Category 1 hurricane territory with widespread structural damage. Small aircraft and most consumer drones are grounded well before that — often by 20–25 mph.
Is 25 mph windy for flying a drone?
For most consumer drones, yes. A DJI-class quadcopter is typically rated for winds up to about 10 m/s (22 mph, Beaufort 5). 25 mph is Beaufort 6, past the safe limit, where the aircraft burns battery fighting the wind and drifts on descent. Check the sustained speed and the gust forecast before launching.