The FFN conversion table tells you the seconds to add to your short-course times to get their long-course equivalent. But the actual gaps are often twice as large. Understanding why — and using the built-in calculator — changes how you prepare your swimmers.
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Distance
Bassin 25m
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Bassin 50m
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The short-course season is over. Your swimmers have posted their best times of the year. Then comes the first long-course competition. The times look catastrophic. A swimmer who was clocking 1'02'' in the 100m freestyle comes out at 1'04''. Another loses 6 seconds on their 200m backstroke. The disappointment is real, and so are the questions.
This is not regression. It is physics. Moving from a short-course pool to a long-course pool mechanically produces slower times. It is not a question of fitness. It is a question of mechanics. And that changes everything about how you should set your January goals.
The answer comes down to one word: turns. And more precisely, what happens after each turn: the streamline.
Each swimming turn breaks down into three phases: the touch of the wall, the push-off, and the underwater streamline. These three phases combined allow the swimmer to reach a speed their arms alone cannot maintain at the surface. Kinematic analyses of underwater phases estimate that a well-executed turn provides an advantage of 0.25 to 0.55 seconds compared to equivalent open swimming.
Over a 100m, the calculation is simple:
That is the basic mechanics. But the actual gap often exceeds this simple calculation for two additional reasons. First, streamline phases are shorter in a long-course pool: swimmers accustomed to long short-course streamlines have to relearn how to manage their speed differently. Second, the physiological aspects change: swimming 400m with only 7 turns instead of 15 stresses the muscles differently, without the propulsive "breaks" that wall push-offs represent.
The French Swimming Federation publishes an official conversion table each year. It indicates the number of seconds to add to a short-course (25m) performance to obtain its theoretical long-course (50m) equivalent. This table is built from the best times recorded worldwide in both pool lengths. It therefore represents the minimum gap observed at the highest level, where turns are executed perfectly and physical condition is at its peak. For any other swimmer, the gap will be larger.
For freestyle, the benchmark stroke, the official values are as follows:
| Event | Seconds to add | Fewer turns |
|---|---|---|
| 50m freestyle | +0.70s | 0 fewer turns |
| 100m freestyle | +1.60s | 2 fewer turns |
| 200m freestyle | +3.40s | 4 fewer turns |
| 400m freestyle | +7.50s | 8 fewer turns |
| 800m freestyle | +16.00s | 16 fewer turns |
| 1,500m freestyle | +30.00s | 30 fewer turns |
Source: FFN 2023 conversion table. Backstroke, breaststroke and butterfly events follow slightly different coefficients. Backstroke and breaststroke are penalized more (underwater streamlines play a greater role), while butterfly transfers better to the long-course pool.
In January 2020, Robin Pla (swimming expert at lepape-info.com) published a unique comparative study: he analyzed the performances of 113 swimmers who were finalists at the French short-course championships in Angers (December 2019), then tracked those same swimmers one week later at long-course meets. A total of 180 races were compared, across all events and strokes.
The actual gap is approximately twice as large as the theoretical FFN table. This is no surprise: the FFN table is built from world records, not from swimmers in their first week of long-course competition, still carrying fatigue from the championships.
But what is more instructive is the difference by stroke. Over 100m, the observed gaps are as follows:
| Stroke (100m) | Men | Women | Interpretation |
|---|---|---|---|
| Butterfly | +1.99s | +2.32s | Smoothest transition |
| Freestyle | +2.44s | ~+2.53s | Within the norm |
| Breaststroke | +3.35s | +3.39s | Difficult transition |
| Backstroke | +3.54s | +3.06s | Hardest transition (M) |
Butterfly transfers best. Backstroke and breaststroke transfer worst, mainly because underwater streamlines play a decisive role in overall speed in those strokes, and those streamlines are more numerous (and therefore more beneficial) in the short-course pool.
Robin Pla also notes a near-symmetrical progression with distance: doubling the distance doubles the gap. This is consistent with turn mechanics, but it means that 400m swimmers and beyond feel the long-course shock with far greater intensity than sprinters.
This data is not just reassuring statistics. It has direct implications for how to plan the final weeks of the short-course season and the first weeks in the long-course pool.
Do not wait for the 50m season to begin before working on long-course-specific qualities. In the final weeks of the winter season, incorporate long sets that break the turn reflex: for example, 6×300m (in a 25m pool) with the instruction not to push off the walls on the last 50 meters of each length. Another option: non-round distances (180m, 350m, 700m), so that swimmers cannot lock onto the wall push-off every 25m as a pace reference.
Your backstroke and breaststroke swimmers need more specific work than your butterfly or freestyle swimmers. The underwater streamline in backstroke — the undulating push-off on the back after each turn — is the most profitable element in the short-course pool. A national-level backstroke swimmer can maintain 3 to 5 meters of streamline at a speed greater than their swimming speed. Losing two turns when moving to the long-course pool means losing 6 to 10 meters of that regime. Plan specific long-course streamline sets from January onwards to limit this loss.
The instinct to taper is understandable before the first 50m competition. But the swimmers in the Robin Pla study were themselves slightly fatigued after the championships, and they still showed gaps twice as large as the FFN table. It is not the level of freshness that explains the gap — it is the lack of specific long-course work. A fatigued swimmer who has trained long sets without wall push-offs will transfer better than a fresh swimmer who has never done them.
After a few seasons, you start to recognize the type. There is the swimmer who comes out of the long-course pool with +2s on their 100m freestyle in the first week, and there is the one who always needs six weeks of competitions before their times start to look like something. This profile barely changes from year to year.
Knowing this individual profile changes how you set goals, how you manage communication with the swimmer, and how you plan competitions at the start of the long-course season. A swimmer who "transfers poorly" should not be entered into a major 50m competition in the first week: they should have a few warm-up meets first.
Building this profile requires historical data: times at the end of the short-course season, then times at the start of the long-course season, year after year. This tracking requires organization, but it is one of the most valuable pieces of information a coach can accumulate about their swimmers over the years. Padlie automatically saves the history of all sessions and performances from the very first season, with nothing to note by hand.
The FFN table tells you where the world's best swimmers have set the bar. It is useful for understanding the mechanics of moving between pool lengths. But for your swimmers, in your club, at the start of the season, it is almost always too optimistic.
Using it as an absolute target for the first long-course competition is setting up for disappointment. Using it as a horizon — "this is what we're aiming for over the season" — gives it its true value.
The real work of the coach is to know each swimmer's habitual gap, to prepare the transition physically, and to calibrate expectations based on stroke and profile. That knowledge, accumulated season after season, is what makes the difference.
Use the FFN conversion table as a starting point, then multiply the theoretical gap by 1.5 to 2 to get a realistic estimate at the start of the long-course season. For 100m freestyle, the FFN table gives +1.60s; the actual gap is often +2.5 to +3.2s during the first competitions.
According to the Robin Pla study (2020), the average gaps observed among finalist swimmers are: +1.22s over 50m, +2.84s over 100m, +5.60s over 200m, +11.16s over 400m. These figures are approximately twice the theoretical values in the FFN table.
Because underwater streamlines play a decisive role in propulsion in backstroke and breaststroke. In a short-course pool (3 turns per 100m), these streamlines account for a much larger share of swim time than in a long-course pool (1 turn). Butterfly transfers better because its streamlines represent a smaller proportion of total swim time.
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