F-Scale Number

Intensity Phrase

Wind Speed

Type of Damage Done

F0

Gale tornado

75 - 120 km/h

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

F1

Moderate tornado

121 - 203 km/h

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 the roads; attached garages may be destroyed.

F2

Significant tornado

204 - 261 km/h

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

F3

Severe tornado

262 - 344 km/h

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

F4

Devastating tornado

345 - 433 km/h

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

F5

Incredible tornado

434 - 529 km/h

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-inforced concrete structures badly damaged.

F6

Inconceivable tornado

529 + km/h

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 identified 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