There are several ways to measure the size of a hurricane, including by death toll, cost, and strength. However, data becomes less available the further back in time one goes, so it’s hard to name a single hurricane that carries the title “worst.”
The storm that caused the most deaths in recorded history was the 1780 “Great Hurricane” in the Lesser Antilles. More than 20,000 people died, according to the National Oceanic and Atmospheric Administration† The agency scores hurricane Mitch, which took place in 1998 and killed more than 9,000 people in Central America, ranks second. Mitch is followed in the rankings by Hurricane Fifi of 1974, which killed more than 8,000 in Honduras, and a hurricane that hit Galveston, Texas, in 1900, killing about 8,000.
In terms of cost, NOAA calls Katrina the most expensive hurricane to hit the United States since 1851, causing $180 billion in damage. That 2005 hurricane was followed by Harvey ($143.8 billion) and Maria ($103.5 billion) in 2017, Sandy ($80 billion) in 2012, and Ida ($76.5 billion) in 2014.
Scientists have also developed several rating systems to calculate a hurricane’s intensity, such as the Saffir-Simpson Scale, which assigns hurricanes to five categories based on wind speed, and the Hurricane Severity Index, which also takes into account the area that may become hit by the winds. When assessing the strength of a hurricane, other indicators, such as barometric pressure and storm surge barrier, may also be considered. Due to the variety of systems and metrics, each approach can yield different results.