100 feet per 3.1 seconds is 21.994135 miles per hour.
Instantly convert feet per second (fps) to miles per hour (mph) using this calculator.
A foot per second is a unit of speed. Something traveling one foot per second is traveling 0.3048 meters per second, or about 0.682 miles per hour.
A mile per hour is a unit of speed commonly used in the United States. It is equal to to exactly 1.609344 kilometers per hour.
See this Feet per Second to Miles per Hour Conversion Table from Calculateme.com.