The Enhanced Fujita Scale (EF Scale) is the standard system used in the United States and Canada to rate tornado intensity. It classifies tornadoes on a six-point scale from EF0 (weakest) to EF5 (strongest) based on damage caused, from which peak 3-second gust wind speeds are inferred.
The scale replaced the original Fujita Scale in the United States on February 1, 2007 and in Canada on April 1, 2013. It was designed to align damage descriptions more accurately with modern engineering knowledge about how structures fail at various wind speeds.
Peels surface off roofs; damages gutters and siding; breaks tree branches; shallow-rooted trees pushed over. About 60% of all tornadoes in the US are rated EF0.
Strips roof surfaces; mobile homes overturned or badly damaged; loss of exterior doors; windows and other glass broken. Beginning of "significant" tornado damage in most classifications.
Roofs torn off well-constructed houses; foundations of frame homes shifted; mobile homes completely destroyed; large trees snapped or uprooted; light-object missiles generated; cars lifted off ground.
Entire stories of well-constructed houses destroyed; severe damage to large buildings such as shopping malls; trains overturned; trees debarked; heavy cars lifted off ground and thrown; structures with weak foundations blown away for some distance.
Well-constructed and whole-frame houses completely leveled; cars and other large objects thrown, and small missiles generated. Even well-built brick homes may be reduced to rubble. This is the intensity of the 2011 Tuscaloosa–Birmingham tornado.
Strong-framed, well-built houses leveled off foundations and swept away; steel-reinforced concrete structures critically damaged; tall buildings collapse or have severe structural deformations; incredible phenomena will occur. Fewer than 0.1% of tornadoes receive this rating. Recent examples: Joplin 2011, Moore 2013, Hackleburg 2011.
EF ratings are assigned by damage survey teams — usually National Weather Service meteorologists — who examine destruction in the tornado's path after the event. The scale uses 28 damage indicators (such as single-family homes, mobile homes, schools, hardwood trees, transmission lines) each with defined degrees of damage. Surveyors compare observed damage to reference photos and assign a wind-speed estimate.
Because the scale is damage-based, a tornado that passes only over open country cannot be rated higher than the strongest damage indicator it happens to hit. This is why some strong tornadoes are underrated: they simply did not encounter a structure capable of documenting their peak intensity.
The original Fujita Scale was developed by Dr. Tetsuya "Ted" Fujita at the University of Chicago in 1971. It also had six categories (F0–F5) but used estimated wind speeds that later engineering research showed were too high — for example, the original F5 required winds over 261 mph, but modern research showed similar damage occurs at 200+ mph. The Enhanced Fujita Scale corrected these estimates without changing the qualitative descriptions.
Modern mobile Doppler radar can directly measure winds inside tornadoes, sometimes recording gusts in excess of 300 mph (the Bridge Creek–Moore 1999 tornado, 301 mph; El Reno 2013, ~296 mph). These measured speeds are typically higher than the EF rating derived from damage. Meteorologists sometimes use the term "high-end EF5" for such tornadoes even when the official rating is limited by damage.
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