Hong Life CalculatorsUnderstanding the Saffir-Simpson hurricane category calculator — concept and principle
The Saffir-Simpson Hurricane Wind Scale rates hurricanes from Category 1 to 5 by their maximum sustained wind and summarises the kind of damage those winds can do. It is the scale used by the US National Hurricane Center for Atlantic and eastern Pacific hurricanes and is widely quoted in news about typhoons too. Enter a 1-minute sustained wind in km/h to get the category and the speed in mph.
How it is calculated
The calculator compares the wind speed v (km/h) with fixed thresholds:
- below 63: tropical depression
- 63–118: tropical storm
- 119–153: Category 1
- 154–177: Category 2
- 178–208: Category 3
- 209–251: Category 4
- 252 or more: Category 5
mph = km/h ÷ 1.609344. The official thresholds are set in mph and knots; the km/h values are their conversions (Category 1 starts at 74 mph or 64 kt).
The principle
Wind pressure on a structure grows with the square of wind speed, so damage rises much faster than the wind. Engineer Herbert Saffir and meteorologist Robert Simpson grouped hurricanes into five bands in the early 1970s, each corresponding to a step up in expected damage, from broken branches and roof shingles in Category 1 to the destruction of many framed homes in Category 5. Since 2010 the scale has been based on wind only; storm surge and central pressure, which were once part of it, were removed because they do not track wind closely enough.
Worked example
- Input: 1-minute sustained wind 200 km/h.
- 200 is at least 178 but below 209, so the storm is Category 3.
- In mph: 200 ÷ 1.609344 = 124.27 mph (124.2742384), inside the official 111–129 mph band for Category 3.
How to read the result
Category 3 and above are called major hurricanes and account for a large share of hurricane damage. A Category 3 can remove roof decking and uproot many trees, and electricity and water may be unavailable for days to weeks. Moving up one category roughly corresponds to a large jump in damage, not a small step. Remember that a weaker storm can still be deadly through flooding and surge.
Common mistakes
- Using a 10-minute mean wind, as many agencies in Asia and elsewhere report, instead of the 1-minute wind the scale is based on; the 1-minute value is typically higher.
- Using gust speeds, which are much higher than sustained winds.
- Assuming the category describes rainfall or storm-surge flooding; it does not.
Frequently asked questions
Is there a Category 6?
No. The scale ends at Category 5 because damage at that level is already catastrophic, although it is sometimes proposed for very intense storms.
What is the difference between a hurricane and a typhoon?
They are the same kind of storm. It is called a hurricane in the Atlantic and northeast Pacific and a typhoon in the northwest Pacific.
Does a lower category mean it is safe?
No. Even Category 1 winds damage roofs and power lines, and slow-moving storms of any strength can cause severe flooding.
Sources: NOAA National Hurricane Center, "Saffir-Simpson Hurricane Wind Scale"