The 70.4 problem
A mile is 1609.344 m. A 25 yard pool is 22.86 m, so a mile is 70.4 lengths — not 66, which is the number many swimmers assume from a 25 m pool. The difference is 4.4 lengths, or about 100 m, which over a season of training is a meaningful discrepancy.
Which mile?
Swimmers sometimes use a 1650 yard “mile” because that is the longest pool event, but a true mile is 1760 yards. The calculator uses the statute mile, so the numbers match running and cycling distances. If your pool counts a 1650 as a mile, subtract about 6% from the result.
Planning a distance
The table gives the length counts for a half mile, a mile, the 1.2 mile 70.3 swim and the 2.4 mile Ironman swim. Use it before a session rather than counting in your head at the wall; losing track at 40 lengths is the most common way to swim the wrong distance.
Frequently Asked Questions
How many laps is a mile in a 25 yard pool?
70.4 lengths, usually rounded to 70 or 72 in training sets.
How many laps is a mile in a 25 m pool?
64.4 lengths.
Is a lap one length or two?
In lap swimming, usually one length. The calculator treats laps as lengths; halve the count if your pool uses round trips.
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