The answer to this perennial pool question depends on the size of the pool
It’s one of the most common questions lifeguards get when working at a pool: How many lengths do I need to swim if I want to complete a mile?
The simple answer is: It depends on the pool.
First, to cover a mile, you’ll have to swim 5,280 feet, or 1,760 yards, or 1,609.34 meters.
Second, not every pool is the same length. Far from it.
In the United States, pools intended for training or competition are typically measured in either yards or meters. A standard competition-sized pool is 25 yards long and is known as a short course yards pool in competitive parlance.
That’s the length of pool used for most summer league, high school, and college competitions. The U.S. never adopted the metric system the rest of the world did, and although international swimming competitions are usually measured in meters, yards rule the day here.
Despite the short length of these pools, you can cover a lot of ground in them. Distance swimmers often refer to the 1650-yard freestyle event, which is 66 lengths, or 33 laps, of a 25-yard pool, as “the mile.” But the event actually falls 110 yards, or 6.25 percent, short of a true mile.
If you want to swim exactly a mile in a 25-yard pool, you’ll need to complete 70.4 lengths of the pool.
Many lifeguards round down to 70 lengths or up to 72 lengths when telling patrons how far a mile is so that you can finish your swim at the same place you left your water bottle and shower shoes.
Although 25-yard pools tend to be more common, it’s not unusual to come across a pool that’s geared for international competition here in the U.S. In such cases, there are usually two options: 25 or 50 meters long.
The shorter 25-meter pools are called short course meters pools. Pools considered “Olympic” pools—because the Olympics are hosted in pools of this length—are 50 meters long and are called long course meters pools.
In a metric meet, the 1500-yard freestyle event is sometimes referred to as “the metric mile.” But it, too, falls short of a true mile, to the tune of 109.34 meters, or 6.8 percent. If you want to swim exactly a mile in a 25-meter pool, you’ll need to swim 64.3736 lengths. Many lifeguards tell patrons to either round down to 64 lengths or up to 66 to keep things simple.
Swimming exactly a mile in a 50-meter pool means completing 32.1868 lengths. Rounding down to 32 lengths will bring you in just under a mile, 34 lengths will give you a little over a mile.
Unusual Shapes and Sizes
If you’re swimming in a hotel, backyard, or other type of pool that’s outside these three standard lengths, you’ll need to do some measuring for yourself or ask the pool operator for assistance. A common measurement for hotel pools is 20 yards, and if you’re swimming in one of these, you’ll need to log 88 lengths to swim a mile.
When it comes to pool measurement for competition, U.S. Masters Swimming has clear rules and protocols for certifying the exact length of a pool to ensure that records can be kept from one pool to the next. The 2021 USMS Rule Book states:
“Measurements must be conducted using a measuring device with a minimum measuring quality of a steel tape over the nominal distance. A laser measuring device may be used, but it must be as accurate as required for steel tapes. The accuracy of the measuring device must provide accuracy of at least ± 0.005 m (± 0.20 in. or 0.016 ft). This tolerance refers to the tolerance of the measuring device only. A pool must always be at least as long as the specified distance in the rule book, which has a minus zero tolerance.”
This is all to prevent your actual mileage from varying and to ensure that the distance you’re signed up for is true to scale.
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