How long do a tornado's winds last?

There are two ways to interpret this question but in both cases the duration can vary greatly.

In terms of how long the tornado itself lasts, most are on the ground for one to five minutes. Major tornadoes, however, often persist for twenty minutes or more and may last for well over an hour.

In terms of how long a given spot is exposed to tornadic winds, it depends on how big the tornado is and how fast it is moving. An "average" tornado is about 100 yards wide and travels at 30 miles per hour, which works out to a duration of about 7 seconds for a given location. A half-mile wide tornado moving at the same speed will take a full minute to pass over a spot. Tornadoes may be stationary or travel at more than 70 miles per hour and can range in size from less than ten yards to more than two miles. One tornado was observed to have stayed in the same place for more than 90 minutes.