Wind Speed: Knots to mph for Sailors and Pilots

June 26, 2025 • 4 min read

Weather reports for sailors and pilots always give wind speed in knots. If you are used to mph or km/h, here is how to make sense of these measurements and understand what they mean for conditions on the water or in the air.

The Conversion

Quick Conversion Reference

• ▶ 5 knots = 5.8 mph = 9.3 km/h (light breeze)
• ▶ 10 knots = 11.5 mph = 18.5 km/h (gentle breeze)
• ▶ 15 knots = 17.3 mph = 27.8 km/h (moderate breeze)
• ▶ 20 knots = 23.0 mph = 37.0 km/h (fresh breeze)
• ▶ 30 knots = 34.5 mph = 55.6 km/h (near gale)
• ▶ 50 knots = 57.5 mph = 92.6 km/h (storm)
• ▶ 64 knots = 73.6 mph = 118.5 km/h (hurricane threshold)

The Beaufort Scale

Admiral Sir Francis Beaufort created this scale in 1805 to standardise wind observations at sea:

• ▶ Force 0 (0-1 kt): Calm — mirror-like sea
• ▶ Force 3 (7-10 kt): Gentle breeze — good sailing for beginners
• ▶ Force 5 (17-21 kt): Fresh breeze — whitecaps, moderate waves
• ▶ Force 7 (28-33 kt): Near gale — sea heaps up, foam streaks
• ▶ Force 9 (41-47 kt): Strong gale — high waves, spray affects visibility
• ▶ Force 12 (64+ kt): Hurricane — devastation

What Wind Speeds Mean in Practice

• ▶ Sailing (dinghy): Ideal conditions 8-15 knots; dangerous above 25 knots
• ▶ Sailing (yacht): Comfortable at 10-20 knots; reef sails above 25 knots
• ▶ Light aircraft: Crosswind limit typically 15-20 knots
• ▶ Commercial aircraft: Crosswind limit around 30-40 knots depending on aircraft
• ▶ Kite surfing: Needs at least 12 knots; ideal 15-25 knots

Why Knots and Not mph?

Since a knot is one nautical mile per hour, and nautical miles relate directly to degrees of latitude on charts, using knots makes navigation calculations simpler. An aircraft flying at 120 knots covers 2 degrees of latitude per hour — that is easy to plot on a chart without any conversion.