Swim time converter: SCY ↔ SCM ↔ LCM
Most converters give you one number and no explanation. This one gives you both methods and the wall count, because the gap between them is not noise — it is the turns, and knowing that is the difference between using a converted time and believing it.
Course conversion — SCY ↔ SCM ↔ LCM
Two methods, both shown, so you can see where the difference comes from.
| Method | 100 LCM | What it assumes |
|---|---|---|
| Distance only | 1:08.35 | Same speed through the water. 100 SCY is 91.44 m, 100 LCM is 100.00 m. |
| Seeding factor | 1:12.44 | The empirical factor meets use to seed swimmers. Fitted to real races, so the average turn effect is already inside it. |
That is the walls. You push off 3 times in a 100 SCY and 1 time in a 100 LCM. A push-off is faster than swimming, so the course with more turns produces the faster clock — the distance-only maths cannot see that, and the seeding factor can.
The three courses
| Code | Means | Pool | Where it is used |
|---|---|---|---|
| SCY | Short course yards | 25 yd (22.86 m) | US high school, college and most US club meets in winter |
| SCM | Short course metres | 25 m | European winter season, world short course championships |
| LCM | Long course metres | 50 m | The Olympic course. Summer season and all major championships |
Method one: distance only
The honest baseline. It assumes you move through the water at the same speed and simply asks how much water there is. A 100 SCY is 91.44 m of swimming; a 100 LCM is 100 m. That is 9.4 % more water, so the time goes up by 9.4 %.
This is exact arithmetic with one enormous blind spot: it thinks a wall is free. It is not — pushing off is the fastest you travel in a race, which is why short course times are faster than the distance alone can explain.
Method two: the seeding factors
These are the numbers meets use to put swimmers in heats when their entry time comes from a different course. They are empirical, fitted to large volumes of real race data, and the average turn effect is already inside them.
| From ↓ / To → | SCY | SCM | LCM |
|---|---|---|---|
| SCY | — | 1.1189 | 1.1591 |
| SCM | 0.8936 | — | 1.0351 |
| LCM | 0.8630 | 0.9661 | — |
Multiply your time by the factor in the row for your course and the column for the one you want. The table is internally consistent — every pair multiplies back to 1 — so converting there and back returns the time you started with.
Why the two answers differ, and which to trust
The difference is the turns, and it grows with distance: a 1500 in a 25 m pool has 59 push-offs against 29 in a 50 m pool. That is why a distance-only conversion looks plausible at 50 m and increasingly wrong at 800 m and beyond.
Use the seeding factor when you need a number someone else will act on — an entry time, a squad group, a comparison against a standard. Use the distance-only number when you want to know how much actual swimming separated two performances, with the wall advantage stripped out.
One caveat that applies to both: these factors are averages across many swimmers. If your underwaters are strong you gain more from short course than the factor assumes, and your converted long course time will flatter you. If your turns are your weakness, the reverse. Either way, the honest read is a range of a couple of seconds, not a single decimal.
Where this fits with the rest of your numbers
If you are converting a time to check a training pace rather than an entry, remember that pace targets are course-specific too. A CSS test done in a 25 m pool will read faster than the same swimmer in a 50 m pool, so convert the test result before applying it to sets in a different pool. And for working out splits at a target pace, the pace calculator does the arithmetic.
Frequently asked questions
Why is my short course time faster than my long course time?
Walls. A push-off is faster than swimming, and a 100 in a 25 m pool gives you three of them against one in a 50 m pool. On top of that, 100 yards is only 91.44 m. Both effects push the short course clock down, which is why a converted time is an estimate rather than an equivalent.
Which conversion method is the official one?
Neither, strictly. Meets seed swimmers using published factor tables, so those are the numbers that decide which heat you swim in, but no governing body claims a converted time is your real time in the other course. Records are only ever set in the course they were swum in.
Is 100 yards the same as 100 metres?
No. A yard is 0.9144 m, so 100 yards is 91.44 m — about 8.5 % shorter. That difference alone accounts for most of the gap between an SCY time and an SCM time over the same nominal distance.
How accurate is a converted time?
Good enough for seeding and for tracking your own progress, not good enough to argue with. Turn quality varies enormously between swimmers: a strong underwater swimmer gains far more from short course than the average factor assumes, and a weak one gains less. Treat the converted number as the middle of a range a couple of seconds wide.
Sources
- Course conversion factors used for meet seeding — Colorado Timing Systems
- Times and course definitions (SCY, SCM, LCM) — USA Swimming
- Facilities rules — pool lengths for record purposes — World Aquatics
SwimFast is an independent publication. We are not a swim school, a coaching service or a governing body, and nothing here is medical advice. Training paces and test protocols are cited from the published research or federation documents linked on each page. Never swim alone, never attempt breath-hold work without supervision, and check with a doctor before starting a new training programme.