F- scale number

Intensity phrase

Wind speed

Type of damage done

F0

Gale tornado

40 -70 mph

Some damage to chimneys; breaks off trees; pushes over shallow-rooted trees; damages sign boards.

F1

Moderate tornado

73-112 mph

The lower limit is the beginning of hurricane wind speed; peels surface off roofs; mobile homes pushed off foundations or overturned; moving autos pushed off road; attached garages may be destroyed.

F2

Significant tornado

113-157 mph

Considerable damage. Roofs torn off frame homes; mobile homes demolished; boxcars pushed over; large trees snapped or uprooted; light object missiles generated.

F3

Severe tornado

158-206 mph

Roof and some walls torn off well constructed houses; trains overturned; most trees in forests uprooted.

F4

Devastating tornado

207-260 mph

Well-constructed houses leveled; structures with weak foundations blown off some distance; cars thrown and large missiles generated.

F5

Incredible tornado

261-318 mph

Strong frame houses lifted off foundations and carried considerable distances to disintegrate; automobile sized missiles fly through the air in excess of 100 meters; trees debarked; steel re-enforced concrete structures badly damaged.

F6

Inconceivable tornado

319-379 mph

These winds are very unlikely. The small area of damage they might produce would probably not be recognizable along with the mess produced by F4 and F5 wind that would surround the F6 winds. Missiles, such as cars and refrigerators would do serious secondary damage that could not be directly attributed as F6 damage. If this level is ever achieved, evidence for it might only be found in some manner of ground swirl pattern, for it may never be identifiable through engineering studies.