Tornadoes are measured using a scale that measures the amount of damage the tornado has caused. It was developed by T. Theodore Fujita of the University of Chicago, USA and this scale is known as the Fujita Tornado Intensity Scale.
F0 or gale tornado: Some damage to chimneys; breaks branches off trees; pushes over shallow-rooted trees; damages sign boards.
F1 or moderate tornado: The lower limit is the beginning of hurricane wind speed; peels surface off roofs; mobile homes pushed off foundations or overturned; moving cars pushed off the roads; attached garages may be destroyed.
F2 or significant tornado: Considerable damage. Roofs torn off frame houses; mobile homes demolished; boxcars pushed over; large trees snapped or uprooted; light object missiles generated.
F3 or severe tornado: Roof and some walls torn off well constructed houses; trains overturned; most trees in forest uprooted
F4 or devastating tornado: Well-constructed houses levelled; structures with weak foundations blown off some distance; cars thrown and large missiles generated.
F5 or incredible tornado: Strong frame houses lifted off foundations and carried considerable distances to disintegrate; car sized missiles fly through the air in excess of 100 meters; trees debarked; steel reinforced concrete structures badly damaged.
F6 or inconceivable tornado: 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.