From distance to lengths
The conversion is distance divided by pool length, rounded up, because you cannot swim a fraction of a length. A 1 mile target needs 71 lengths in a 25 yard pool, not 70.4 — the extra length is the difference between finishing the set and stopping 9 m short. 25 yard pool laps are where most counting errors start, because a yard pool is 22.86 m rather than 25 m. 50 meter pool laps are the easy case: 2 km is exactly 40 of them.
Time the set before you start
If you add a pace per 100 m, the calculator gives the total time, which is more useful than the length count for planning a session. Two kilometres at 2:00 per 100 m is 40 minutes of swimming, plus rest — and rest is usually 10–15% on top for a set of 100s.
Pool length changes everything
The same 2 km is 80 lengths in a 25 m pool, 40 in a 50 m pool and 87.5 in a 25 yard pool. If you switch pools, re-run the number rather than assuming your usual 60 lengths is still 1500 m.
Frequently Asked Questions
How many lengths is 1 km?
40 in a 25 m pool, 20 in a 50 m pool, 43.7 in a 25 yard pool.
Should I round up or down?
Up. Stopping short is worse than swimming one extra length.
Does the time include rest?
No — it is swim time only. Add 10–20% for rest depending on the set.
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.