The Fujita-Pearson Scale of Tornado Intensity was developed in the early 1970's by T. Theodore Fujita of the University of Chicago and Allen Pearson, director of NSSFC, to measure wind speed, path length and path width in tornadoes according to the damage they produce.
F0 - LIGHT DAMAGE
Wind speeds 40-72 miles per hour.
Tornado will cause some damage to chimneys, break twigs and branches off trees, push over shallow-rooted trees, damage signboards, and break some windows.
F1 - MODERATE DAMAGE
Wind speeds 73-112 miles per hour.
Tornado will peel surfaces off roofs, overturn or push mobile homes off foundations, demolish outbuildings, push moving autos off the roads, and snap or break trees.
F2 - CONSIDERABLE DAMAGE
Wind speeds 113-157 miles per hour.
Tornado will tear roofs off frame houses, demolish mobile homes, lift and move frame houses with weak foundations, snap or uproot large trees, and generate light object missiles.
F3 - SEVERE DAMAGE
Wind speeds 158-206 miles per hour.
Tornado will tear roofs and some walls off well-constructed houses, overturn trains, uproot most trees in a forest, lift off the ground and throw heavy cars, and blow weak pavement off roads.
F4 - DEVASTATING DAMAGE
Wind speeds 207-260 miles per hour.
Tornado will level well-constructed houses, blow structures with weak foundations off some distance, throw and disintegrate cars, uproot trees in a forest and carry them some distance away.
F5 - INCREDIBLE DAMAGE
Wind speeds 261-318 miles per hour.
Tornado will lift strong frame houses off their foundations and carry them considerable distances to disintegrate, propel automobile-sized missiles through the air in excess of 300 feet, debark trees, and create incredible phenomena.
