Fujita Scale

The official classification system for tornado damage. The scale ranges from F0 (gale tornado, minor damage, winds up to 72 mph) to F5 (devastating tornado, winds 261 to 318 mph). In the United States and in some other countries, on February 1, 2007, the Fujita scale was decommissioned in favor of what scientists believe is a more accurate Enhanced Fujita Scale, which replaces it.

(or F Scale) - A scale of tornado intensity in which wind speeds are inferred from an analysis of wind damage:

All tornadoes, and most other severe local windstorms, are assigned a single number from this scale according to the most intense damage caused by the storm.