The Saffir-Simpson Hurricane Wind Scale rates a hurricane’s strength from 1 to 5. A hurricane’s sustained wind speed determines a hurricane’s category. This helps estimate potential property damage along a hurricane’s path.

A hurricane is a tropical cyclone. Tropical cyclones are strong, rotating storms that begin over tropical oceans and bring strong winds and heavy rain. When a tropical cyclone in the northeastern Pacific or the North Atlantic reaches wind speeds of 119 kilometers (74 miles) per hour, it’s called a hurricane. Tropical cyclones in the northwest Pacific Ocean are called typhoons.

Meteorologists use the Saffir-Simpson scale to rank tropical cyclones in the northeastern Pacific Ocean and north Atlantic Ocean. This includes the Gulf of Mexico and Caribbean Sea. Category 3, 4, and 5 hurricanes are major hurricanes and cause the most damage in the United States. Yet category 1 and 2 hurricanes can still inflict major destruction.

The scale doesn’t include hurricane-related damage from storm surges, floods, and tornadoes. One of the deadliest hurricanes in U.S. history (and the costliest) was Katrina, which hit Louisiana in August 2005 at category-3 strength. Katrina took the lives of more than 1,500 people. Many of those deaths were from the hurricane’s destructive storm surge.

Here are the category specifics:

Category 1: Wind speeds are between 119–153 kilometers (74–95 miles) per hour. Very dangerous winds will produce some damage. Homes will have roof damage, and large branches of trees will fall to the ground. Power lines and poles may be damaged, causing power outages that could last between a few and several days.

Category 2: Wind speeds between are 154–177 kilometers (96–110 miles) per hour. Extremely dangerous winds will cause extensive damage. Well-built homes could have major roof damage and many shallowly rooted trees will be uprooted and block roads. Power outages could last anywhere between several days to weeks.

Category 3: Wind speeds are between 178–208 (111–129 miles) kilometers per hour. High winds will cause devastating damage. Well-built homes may have extensive roof damage, and many trees will be uprooted or snapped, blocking roads. Utilities such as electricity and water will be unavailable for several days to weeks.

Category 4: Wind speeds are between 209–251 kilometers (130–156 miles) per hour. Catastrophic damage will occur. Homes may lose most of their roofs and some exterior walls, and most trees will be uprooted or snapped. Fallen power poles and trees will isolate residential areas. Power outages may last weeks to possibly months. Most of the area will be uninhabitable for weeks or months.

Category 5: Wind speeds are greater than or equal to 252 kilometers (157 miles) per hour. Winds at this speed will cause catastrophic damage. Many homes will be devastated, with total roof failure and collapsed walls. Fallen trees and power poles will isolate residential areas. Power outages will last for weeks to possibly months. Most of the area will be uninhabitable for weeks or months.