The Fujita scale

It is very difficult to measure the power or windsspeed of a tornado. First of all you must have the luck to be at the right place on the right time with the right equipment. Secondly the measuring-instruments must be able to stand the enormous powers of a tornado.

Ted Fujita
However, Ted Fujita has found a way to classify tornadoes. Not through wind speed or power, but by searching for a pattern in the damage that a tornado leaves behind. This scale is known as the Fujita scale or the F-scale.

Disadvantages
The F-scale has some disadvantages. Firstly it is based on the damage a tornado does and not on the wind speed of a tornado. The speeds that are showed in the scheme below are just a estimation and are until now never proved. But there is a much bigger disadvantage about the Fujitascale. For example when a tornado with a funnel from 800 meters travels over farm land, it won't get a F-scale ranking, because there wasn't much damage done. When this tornado happened in a big city it could get a F4 ranking.

Substitute
In spite of these disadvantages this scale is used worldwide. Simply because there isn't a good substitute. And true storm chasers can see what F ranking the tornado should have, independent of the fact that the tornado rages over farmland instead of over New York.

F-ranking	Wind speed	Damage
F0	64 to 116 kmh	Light damage. Damage to chimneys,tree branches break off, shallow-rooted trees pushed over, sign-boards damaged.
F1	117 to 180 kmh	Moderate damage. Roof-tiles peeled off, mobile homes pushed or overturned, moving cars pushed off the roads.
F2	181 to 253 kmh	Considerable damage. Roofs of frame houses torn off, mobile homes demolished, large trees snapped or uprooted; light-objects turn into missiles.
F3	254 to 331 kmh	Severe damage. Roofs and some walls torn off well-constructed houses, trains pushed out of their rails, almost every tree uprooted, heavy cars lifted up and thrown through the air.
F4	332 to 418 kmh	Devastating damage. Well-constructed houses leveled, structures with weak foundation blown away, cars thrown and turned into large missiles.
F5	419 to 507 kmh	Incredible damage. Strong frame houses lifted off foundations and carried considerable distance to disintegrate, automobile sized missiles fly a large distance through the air, trees debarked, incredible phenomena will occur.
F6	508 and faster kmh	Iconceivable damage. A F6 tornado has never been observed. It is a theoretical value for the strongest tornado possible.