Here is the system as originally presented by NOAA:
Fujita Tornado Damage Scale
Developed in 1971 by T. Theodore Fujita of the University of Chicago
|Scale||Wind Estimate *** (MPH)||Typical Damage|
|F0||< 73||Light damage. Some damage to chimneys; branches broken off trees; shallow-rooted trees pushed over; sign boards damaged.|
|F1||73-112||Moderate damage. Peels surface off roofs; mobile homes pushed off foundations or overturned; moving autos blown off roads.|
|F2||113-157||Considerable damage. Roofs torn off frame houses; mobile homes demolished; boxcars overturned; large trees snapped or uprooted; light-object missiles generated; cars lifted off ground.|
|F3||158-206||Severe damage. Roofs and some walls torn off well-constructed houses; trains overturned; most trees in forest uprooted; heavy cars lifted off the ground and thrown.|
|F4||207-260||Devastating damage. Well-constructed houses leveled; structures with weak foundations blown away some distance; cars thrown and large missiles generated.|
|F5||261-318||Incredible damage. Strong frame houses leveled off foundations and swept away; automobile-sized missiles fly through the air in excess of 100 meters (109 yds); trees debarked; incredible phenomena will occur.|
For more information, visit NOAA’s Online Tornado FAQ.
*** IMPORTANT NOTE ABOUT F-SCALE WINDS: Do not use F-scale winds literally. These precise wind speed numbers are actually guesses and have never been scientifically verified. Different wind speeds may cause similar-looking damage from place to place — even from building to building. Without a thorough engineering analysis of tornado damage in any event, the actual wind speeds needed to cause that damage are unknown. The Enhanced F-scale was implemented February 2007 in the United States and 2013 in Canada.