Definition of the Fujita Tornado Scale - developed by Professor Theodore Fujita of the University of Chicago to classify tornadoes according to wind speed and damage.
(FO) Gale Tornado (40 - 72 mph)
Light damage: some damage to chimneys, breaks branches off trees, pushes over shallow-rooted trees, and damages sign boards.
(F1) Moderate Tornado (73 - 112 mph)
Moderate damage: The lower limit (73 mph) is the beginning of hurricane wind speed, peels surfaces of roofs, mobile homes pushed off foundations or overturned, and moving autos pushed off roads.
(F2) Significant Tornado (112 - 157 mph)
Considerable damage: Roofs torn off the frames of houses, mobile homes demolished, boxcars pushed over, large trees snapped or uprooted, and heavy cars lifted off ground and thrown
(F3) Severe Tornado (158 - 206 mph)
Severe damage: Roofs and some walls torn off well-constructed houses, trains overturned, most trees in forest uprooted, and heavy cars lifted off ground and thrown.
(F4) Devastating Tornado (207 - 260 mph)
Devastating damage: Well-constructed houses leveled, structures blown off weak foundations, and cars and other large objects thrown about.
(F5) Incredible Tornado (261 - 318 mph)
Incredible damage: Strong frame houses are lifted off foundations and carried a considerable distance and disintegrated, automobile sized missiles fly through the air in excess of 100 meters, and trees debarked.
(F6+) Inconceivable Tornado (319 - 379 mph)
The maximum wind speed of tornadoes is not expected to reach the F6 wind speeds.