Hurricane Category Calculator: Saffir–Simpson Category from Wind Speed

How it works

Category from the 1-minute maximum sustained wind (NHC): Tropical depression ≤ 38 mph · Tropical storm 39–73 mph (34–63 kt, 63–118 km/h) · Cat 1 74–95 mph (64–82 kt, 119–153 km/h) · Cat 2 96–110 mph (83–95 kt, 154–177 km/h) · Cat 3 111–129 mph (96–112 kt, 178–208 km/h) · Cat 4 130–156 mph (113–136 kt, 209–251 km/h) · Cat 5 ≥ 157 mph (≥ 137 kt, ≥ 252 km/h) · 1-minute wind ≈ 1.12 × 10-minute wind · peak gust ≈ 1.3 × sustained · wind force ∝ v²

The Saffir–Simpson Hurricane Wind Scale rates a hurricane from 1 to 5 by its maximum sustained surface wind, averaged over 1 minute at 10 m height. Category 3 and above are major hurricanes. The National Hurricane Center publishes each range in mph, knots and km/h. Those ranges are rounded separately, so the calculator compares your number with the range for the unit you chose; m/s values are converted to knots, the unit forecasters work in. The scale says nothing about storm surge, rainfall or tornadoes, which often do more harm than the wind. Most agencies outside the US (the WMO standard, Japan, India, Australia and others) average wind over 10 minutes, which reads lower for the same storm. Choose the 10-minute option and the calculator multiplies by about 1.12, NOAA’s rule of thumb, before classifying. Gusts last a few seconds and, in a hurricane, typically run about 30% above the 1-minute wind (NOAA HRD). Wind force rises with the square of speed, so a 130 mph Category 4 pushes about 3 times as hard as a 74 mph Category 1, and the wind’s power rises with the cube. The original scale also listed central-pressure ranges for each category. NHC dropped them in 2010 because pressure and wind do not line up closely enough, so they are shown only as a historical reference.

Worked example

A storm with 130 mph maximum sustained winds is 209 km/h, 113 kt or 58.1 m/s. That is the bottom of the Category 4 range (130–156 mph), a major hurricane with catastrophic damage. Peak gusts are about 1.3 × 130 = 169 mph, the wind pushes (130 ÷ 74)² = 3.1 times as hard as a minimal Category 1, and it needs another 27 mph (157 mph) to become a Category 5.

Sources: NOAA National Hurricane Center: Saffir–Simpson Hurricane Wind Scale · NOAA AOML Hurricane Research Division FAQ D4: sustained winds, gusts and averaging periods · WMO: Classification of tropical cyclones (averaging-period conversion guidance)

Frequently asked questions