Length: Most outdoor lap pools in the world are measured in metres, but in the United States outdoor lap pools are often measured in feet and yards. In the UK most pools are calibrated in metres, but older pools measured in yards still exist. In the US, pools tend to either be 25 yards (SCY-short course yards), 25 metres (SCM-short course metres) or 50 metres (long course). US high schools and the NCAA conduct short course (25 yards) competition. There are also many pools 33⅓ m long, so that 3 lengths = 100 m. This pool dimension is commonly used to accommodate water polo.
USA Swimming (USA-S) swims in both metric and non-metric pools. However, the international standard is metres, and world records are only recognized when swum in 50 m pools (or 25 m for short course) but 25-yard pools are very common in the US. In general, the shorter the pool, the faster the time for the same distance, since the swimmer gains speed from pushing off the wall after each turn at the end of the pool.
Width: Most European pools are between 10 m and 50 m wide.
Depth: The depth of a swimming pool depends on the purpose of the pool, and whether it is open to the public or strictly for private use. If it is a private casual, relaxing pool, it may go from 1.0 to 2.0 m (3.3 to 6.6 ft) deep. If it is a public pool designed for diving, it may slope from 3.0 to 5.5 m (10 to 18 ft) in the deep end. A children’s play pool may be from 0.3 to 1.2 m (1 to 4 ft) deep. Most public pools have differing depths to accommodate different swimmer requirements. In many jurisdictions, it is a requirement to show the water depth with clearly marked depths affixed to the pool walls.