Named for its use in the Olympic Games, an Olympic-size swimming pool is 50 m long and 25 m wide.
Though, some competition pools might technically be longer than 50 m, to accommodate touch panels. According to the official governing body, FINA, the measured distance between touch panels must equal 50 m in order for the pool to be suitable for competition.
All Olympic-size pools are required to be at least 1 m deep, with extra depth at the walls, but if the pool will be used for the Olympic Games or World Championships, it needs to be at least 2 m deep. An Olympic-size pool with a depth of 2 m will hold 660,000 gallons of water.
All lanes must be 2.5 m wide, with extra space on the sides of the pool. Depending on the intended use, pools will either have eight or ten lanes. Eight-lane pools are used in World Championship races and ten-lane pools are used in the Olympic Games. The list of regulations is long and detailed, covering everything from water temperature to lighting; you can find the complete list of rules here.
Many athletes prefer 50 m pools for training because the distance helps build endurance, simulates an open water situation and helps them get into a rhythm. Other athletes train in 25 m pools to improve their speed.