Forecasters and researchers use a wind damage scale to classify tornadoes.
The original Fujita scale was developed by T. Theodore Fujita and was put into use in 1973. The scale was
enhanced in 2007, with rankings running from EF (Enhanced Fujita) - 0 through 5. The ratings are based on
the amount and type of wind damage
The Fujita Tornado Intensity Scale:
F0 - Gale With winds of less than 73 miles per hour
F1 - Moderate With winds from 73 to 112 mph
F2 - Significant With winds from 113-157 mph
F3 - Severe With winds from 158-206 mph
F4 - Devastating With winds from 207-260 mph
F5 - Incredible With winds from 261-318 mph
F6 - Inconceivable With winds above 318 mph
EF-0. Light damage Wind 65 to 85 mph.
EF-1. Moderate damage Wind 86 to 110 mph.
EF-2. Considerable damage Wind 111 to 135 mph.
EF-3. Severe damage Wind 136 to 165 mph.
EF-4. Devastating damage Wind 166 to 200 mph.
EF-5. Incredible damage Wind above 200 mph.
It should be noted that the Enhanced F-scale is a set of wind estimates (not measurements) based on damage.
It uses three-second estimated gusts estimated at the point of damage