Competitive swimming can be done in three different length pools: 50 Meter “Olympic Size” pools, 25 Meter Pools, and 25 Yard “NCAA Size” Pools. These lengths are known as Long Course Meters (LCM), Short Course Meters (SCM), and Short Course Yards (SCY), respectively.

In theory, while there are differences between swimming a long course and short course race, mainly surrounding the reduced turn—and therefore underwater—count, times should be convertible, so that one could compare a swim in one type of pool to another time in another type of pool, such as a Short Course Yards to Short Course Meters. High-level competitive meets require a swimmer to qualify by beating a specific qualifying time in an event. If the qualification times are provided in short course, for example, but the swimmer swims a race in long course, often the swimmer wants to compare their performance with the qualification time in a different pool length.