Count lengths, not round trips
Most lap swimmers count lengths — one trip up the pool — while some watches call a round trip a lap. Sixty lengths in a 25 yard pool is 1500 yards, or 0.85 miles. If your count is off by a factor of two, the pace will be off by the same factor, so check which convention your pool uses.
Pool size changes the number
One hundred lengths of a 25 yard pool is 2286 m; the same count in a 25 m pool is 2500 m. That is a 9% difference, enough to make a training partner's pace look better than it is. The calculator converts your count to metres first, so the per-100 figure is comparable across pools.
Turns are free speed
A 25 m pool has twice as many turns as a 50 m pool, and each push-off is worth roughly a second. Short-course times are therefore faster than long-course times over the same distance, which is why comparisons should always state the pool length.
Frequently Asked Questions
Does a lap mean one length or two?
In most lap-swimming usage, one lap is one length. Competitive pools and some watches use round trips — check before comparing times.
How many lengths is a mile?
70.4 lengths of a 25 yard pool, or 64.4 lengths of a 25 m pool.
Why does per-length pace matter?
It is the number you can control in a set: hold 30 seconds per 25 m and the 100 m pace takes care of itself.
Related tools
Privacy & your data
SwimRunPace calculates everything in your browser. Distances, times and body weights are never uploaded — there is no account, no server-side record and no training history stored between visits.