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Enhanced Fujita Scale
The Fujita Scale Intensity Rating
The original Fujita scale (F-scale) was replaced with the Enhanced Fujita Scale on February 1, 2007. The Enhanced F-scale is still a set of wind estimates (not measurements) based on damage.

It uses three-second gusts estimated at the point of damage based on a judgment of 8 levels of damage to 28 indicators. These estimates vary with height and exposure.

Important note
The 3 second gust is not the same wind as in standard surface observations. Standard measurements are taken by weather stations in open exposures, using a directly measured, "one minute mile" speed. The scale uses actual damage to determine a tornado’s wind speed.

The Enhanced Fujita Scale