F0:40-72 mph
F1:73-112 mph
F2:113-157mph
F3:158-206 mph
F4:207-260mph
F5:261-318 mph
Note: A tornado is deemed a funnel cloud, until it actually touches the ground and generally forms from the southwest edge of a storm. A tornado is many times accompanied by hail and stronger than hurricane force winds. The debris thrown about along its path can be deadly.
Keep in mind that while this scale is based on winds, it is also based on damage assessment after the fact. A caution
here is that the quality of construction of the damaged structure can make the winds appear stronger than they actually were.