What wind speed in knots marks the start of hurricane strength?

A sustained wind speed of 64 knots marks the start of hurricane strength on the Saffir–Simpson hurricane wind scale.

That threshold equals 74 mph or 119 km/h and is based on the storm’s maximum one-minute average sustained wind measured 10 meters above the surface. At 64 to 82 knots, a storm is classified as a Category 1 hurricane. Stronger winds move it into Categories 2 through 5.

The scale was developed in the early 1970s by civil engineer Herbert Saffir and meteorologist Robert Simpson. It is designed for hurricanes in the Atlantic and northeastern Pacific, where one-minute sustained winds are the standard used for the scale. Category 5 begins at 137 knots, or 157 mph.

A frequent source of confusion is that tropical cyclone agencies around the world use different averaging periods and classification systems. Some regions use 10-minute sustained winds, and a storm called a typhoon or severe tropical cyclone may be measured differently. Thus, 64 knots is the standard hurricane threshold, not a universal threshold for every regional cyclone label.