Wind Speed and Beaufort Converter

Convert wind speed between the Beaufort scale, km/h, mph, knots, and m/s.
Includes sea state and land effect descriptions for each Beaufort force level.

Type a speed in any field and the others update instantly, or pick a Beaufort force.
The panel below gives the sea state, the wave height, and what it does on land.

Wind Force
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Enter a wind speed, or pick a Beaufort force.

The Beaufort scale classifies wind speed by observed conditions.

Speed conversions:

  • 1 knot = 1.852 km/h = 1.15078 mph = 0.51444 m/s
  • 1 m/s = 3.6 km/h = 2.23694 mph = 1.94384 knots

Beaufort scale reference:

Force Description km/h mph knots m/s
0 Calm 0–1 0–1 0–1 0–0.2
1 Light air 1–5 1–3 1–3 0.3–1.5
2 Light breeze 6–11 4–7 4–6 1.6–3.3
3 Gentle breeze 12–19 8–12 7–10 3.4–5.4
4 Moderate breeze 20–28 13–18 11–16 5.5–7.9
5 Fresh breeze 29–38 19–24 17–21 8.0–10.7
6 Strong breeze 39–49 25–31 22–27 10.8–13.8
7 Near gale 50–61 32–38 28–33 13.9–17.1
8 Gale 62–74 39–46 34–40 17.2–20.7
9 Strong gale 75–88 47–54 41–47 20.8–24.4
10 Storm 89–102 55–63 48–55 24.5–28.4
11 Violent storm 103–117 64–72 56–63 28.5–32.6
12 Hurricane 118+ 73+ 64+ 32.7+

Beaufort 6+ can make walking difficult. Beaufort 8+ can cause structural damage.

Sea state and wave height

The scale was written for sailors, and the sea column is the original one. Wave heights assume open water with the wind having blown steadily for long enough to raise a full sea, which is why a gale in a sheltered bay looks nothing like a gale in the Atlantic.

Force Sea state Wave height (m)
0 Sea like a mirror 0
1 Ripples, no foam crests 0.1
2 Small wavelets, glassy crests 0.2
3 Large wavelets, scattered whitecaps 0.6
4 Small waves, frequent whitecaps 1.0
5 Moderate waves, many whitecaps, some spray 2.0
6 Large waves, extensive foam crests, spray 3.0
7 Sea heaps up, foam blown in streaks 4.0
8 Moderately high waves, crests break into spindrift 5.5
9 High waves, dense foam, spray affects visibility 7.0
10 Very high waves, sea surface white, visibility reduced 9.0
11 Exceptionally high waves, sea covered in foam patches 11.5
12 Air filled with foam and spray, sea completely white 14+

What it means on land

Force 6 is where a beach umbrella becomes a problem and cycling into the wind stops being fun. Force 7 makes walking noticeably hard. Force 8 breaks twigs off trees and is the point most small-craft operations stop.

Force 9 and above is genuinely dangerous outdoors: slates come off roofs, and the risk is being hit by something rather than being blown over.

Where the numbers came from

Francis Beaufort, an officer in the Royal Navy, standardised the scale in 1805. His version had nothing to do with speed. It described how much sail a full-rigged man-of-war could carry, running from “just sufficient to give steerage way” up to “that which no canvas could withstand”. Speeds were attached much later, in 1946, which is why the bands are uneven and land in awkward numbers in every unit.

That history explains the scale’s odd durability. It is an observational scale, so a sailor with no instrument can still report a useful number by looking at the water, and it compresses a huge range into thirteen memorable steps.

How we build and check this converter

This converter runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.

SuperGlobalCalculator is independently built and maintained. See how we build and verify our calculators.

Calculated with Super Global Calculator at SuperGlobalCalculator.com

Wind Speed and Beaufort Converter, printed 2026-09-08

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