Neither. Say, "25 metre pool".
A semi-olympic pool is 25 meters long by 12.5 meters wide with a depth of between 1.2 and 1.6 meters.
100cm by 200cm
In Europe, the answer is unequivocally 50 meters. However, in the United States the term "Olympic size pool" usually refers to a pool that is half that size, or 25 meters.
An Olympic pool is 50 metres long so half a mile = 16.1 laps approx.
An Olympic Length pool is 50 meters. To convert any meter to feet, you multiply by 3.28084, so an Olympic Length pool should be 164.02 feet or 54.68 yards. addendum: for extra trivia - an Olympic pool is 25 meters wide and 2 meters deep. Use the same conversion factor as mentioned above.