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25, 33 or 50 m pool: how to adapt a swim workout

Most swim workouts are written with a 25 m pool in mind. But you may end up in a 33 m pool, or a 50 m one. On paper the workout stays the same. In the water it does not. Here is what changes and how to adapt a session without making up numbers.

Why the same workout feels different

The main difference is how many walls you meet. Each wall is a turn: you slow down, rotate, push off with your feet and get going again. In 100 metres, not counting the start:

  • in a 25 m pool: 4 lengths and 3 turns
  • in a 33 m pool: 3 lengths and 2 turns
  • in a 50 m pool: 2 lengths and 1 turn

Fewer turns means fewer push-offs and fewer short pauses, so in a long pool you swim longer stretches without a break. Your technique and endurance show more, and your turns matter less.

That is also why times are not directly comparable. Race data generally show faster times in short course than in long course, with the gap widest in backstroke and breaststroke. How big it is depends on stroke, distance and how good your turns are. A 100 in a 25 m pool and a 100 in a 50 m pool cannot be compared, or converted with one exact factor.

How to convert distances

In a 33 m pool the repeats in the workout do not land on a wall. The easiest method is to count lengths.

  • Workout (25 m pool): 100 m. 33 m pool: 3 lengths. Metres swum: 99 m.
  • Workout (25 m pool): 200 m. 33 m pool: 6 lengths. Metres swum: 198 m.
  • Workout (25 m pool): 400 m. 33 m pool: 12 lengths. Metres swum: 396 m.
  • Workout (25 m pool): 50 m. 33 m pool: 1 length (33 m) or 2 lengths (66 m). Metres swum: 33 m or 66 m.
  • Workout (25 m pool): 25 m. 33 m pool: 1 length. Metres swum: 33 m.

The 100, 200 and 400 come out almost the same: 99, 198, 396 metres, which is 1% less. Not worth worrying about. For the 50 and the 25 you have to choose whether to round down or up. The 25 becomes a full 33 m length, which is 32% longer, so it is not equivalent.

Worked example

The workout says 8 x 100 free @2:00 for a 25 m pool. In a 33 m pool it becomes 8 x 3 lengths, which is 8 x 99 m = 792 metres instead of 800. You are 8 metres short, one per repeat. That is fine. There is no need to make up the missing metres.

What about 8 x 50 free, 20 s rest? Two choices: 8 x 1 length (264 m in total, 34% less than the 400 m written) or 8 x 2 lengths (528 m, 32% more). Pick based on how you feel and on the rest of the session.

How to adapt paces and send-offs

There is no universal official rule for converting times between pools of different lengths. If a coach or federation uses one, it applies to their context, and it depends on stroke and distance. We do not invent one here. What you can do in practice:

  1. Keep the written send-off the first time. With 99 m instead of 100 the distance changes by 1%, which is almost nothing.
  2. Watch how much rest you get. If you rest too little, lengthen the send-off a bit. If you stand around for a long time, shorten it.
  3. Use your own times. After a few sessions in the same pool you have your own reference, much more reliable than a theoretical conversion.
  4. Do not compare times across pools. To see progress, always use the same pool.

If the workout gives a fixed rest (20 s rest), you do not need to change anything: the rest is the same in any pool.

When the workout is written for 25 m and your pool is 33 m

A simple routine:

  • Convert the distances by counting lengths, as in the table.
  • Keep the same number of repeats.
  • Keep the same send-off or rest. Then adjust by feel.
  • If the workout has 25 m repeats (technique drills, for example), swim one full 33 m length: slightly longer, same work.
  • Write your times down: after a few sessions you will know your pace in that pool.

What about a 50 m pool?

The same logic runs the other way. 100 m is 2 lengths. 25 m drills become half a length: you can stop halfway, or swim a full 50 m length. With one turn per 100 m, short rests can feel harder, because you no longer get the wall every 25 metres. If you have always swum in 25 m pools, allow a bit more rest in the first sessions.

What does not change

Technique, breathing and the overall plan stay the same. Only the numbers on the wall change. If workout notation is still unclear, start with our guide to reading a swim workout. For a reference pace built from your own times, see the article on critical swim speed, and always do the test in the same pool.

A plan that adapts

SwimSensei builds a plan from your level, the days you train and your pool length (25, 33 or 50 m), and adapts it every week. See how it works on the swimmers page and ask for early access.

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