Swimming Set Generator

What this generator does

Builds a session in metres, which is what makes it different from every other training tool here. The interval generators arrange time — work, rest, repeat. A swim set is measured in distance, has to come out in whole lengths of the pool you are actually in, and has send-offs that must exceed the time the swim takes. All three are arithmetic the minute-based planners cannot do.

How to use this tool

1. Set the distance you want to swim and your pool length.
2. Add your easy pace per 100 m if you want send-off times.
3. Tick the strokes you are happy to swim.
4. Build the session, or seed it to get the same one back.

Understanding the controls

Session distance

Rounded to whole lengths of your pool, and the sets then add up to exactly that. A 2,000 m target in a 33 m pool becomes 1,980 m, and the page says so rather than writing a set you cannot swim.

Pool length

20, 25, 33 or 50 metres. This is the constraint everything else is built around — every repeat distance is a whole number of lengths, so nothing ends up half a length from the wall.

Your easy pace per 100 m

Used to work out send-off times. Turn it off and you get the distances alone, which is what most people want if they are not swimming on a clock.

Strokes

Sets are only drawn from the strokes you tick, so a freestyle-only session never asks you to swim butterfly.

Seed

A word reproduces the identical session, which is useful for repeating a week.

Worked examples

1,500 m in a 25 m pool

Five phases totalling exactly 1,500 m, every repeat a whole number of lengths.

2,000 m in a 33 m pool

Becomes 1,980 m — 60 lengths — and says why.

Pace of 2:00 per 100 m

A 100 m repeat gets a send-off of 2:20, never 2:00.

The same seed

The identical session, set for set.

Common use cases

• Turning up at the pool with a plan instead of swimming lengths
• Building a session around a distance target rather than a time
• Getting send-off times without doing the arithmetic on the poolside
• Varying a session that has become the same 1,500 m every week
• Writing a session for a 33 m or 50 m pool where the usual numbers do not divide

How this generator works

The distance is converted to whole lengths and shared across five phases by largest remainder, so the phases sum to the session exactly. Each phase draws a set type and splits its lengths into whole repeats, with any remainder becoming a shorter final repeat rather than being dropped. Send-offs are your pace for the repeat distance plus a rest allowance, rounded up to the next five seconds because that is how a pace clock is read. A set with no rest — the cool-down — gets no send-off at all, because a cool-down is not swum against a clock.

Randomness and fairness

Randomness picks which set type fills each phase and which stroke it uses. The distances, the phase split and the send-off arithmetic are all derived, so pressing again gives a different session of exactly the same length. A seed makes the choice reproducible through a documented non-cryptographic generator.

For how randomness is produced across the whole site, see how Generate Random works.

Assumptions this tool makes

• You can swim the strokes you ticked, and the pool is free enough to hold a send-off.

Limitations and good to know

• It arranges distances. It is not coaching, not a training plan, and knows nothing about you beyond the pace you typed.
• Pace is treated as linear, so the send-off for a 400 m repeat assumes you hold your 100 m pace — most swimmers do not.
• It has no idea of your technique, so a drill it offers may not be one you should be doing unsupervised.
• Equipment is not modelled: no pull buoys, paddles or fins in the sets.
• Nothing is saved between visits — note the seed if you want the session back.

Common mistakes

Taking a set written for 25 m into a 50 m pool

Set the pool length first. A 150 m repeat is six lengths in a 25 m pool and three in a 50 m pool, and only one of those is swimmable as written.

Setting a send-off from your best 100 m time

Use your easy pace. A send-off built on race pace is one you will miss by the third repeat.

Skipping the cool-down because it has no send-off

It has none deliberately — it is swum easy until your breathing settles, not against a clock.

Practical tips

• Write the session on a waterproof card or a slate; nobody remembers a main set after the second repeat.
• If you keep missing a send-off, the pace you entered is your race pace rather than your easy one.
• Seed a session you liked and swim it again in a fortnight to see whether the same pace feels easier.

Privacy and your data

Everything is computed in your browser from the distance, pool length and pace you set. There is nothing to upload, nothing is stored between visits, and none of your settings are written into the page address. Analytics records that the tool ran and how many sets it produced.

Frequently asked questions

What changed here?

It used to suggest a single set. It now builds a whole session — warm-up through to cool-down — in whole lengths of your pool, adding up to the distance you asked for, with send-off times if you want them.

Why did my distance change slightly?

Because a session has to be a whole number of lengths. In a 33 m pool, 2,000 m is not, so it becomes 1,980 m and the page tells you.

How are send-off times worked out?

Your pace for that repeat distance, plus a rest allowance, rounded up to the next five seconds. The send-off is always longer than the swim — a set you cannot make is not a hard set, it is a broken one.

Is this a training plan?

No. It arranges distances into a sensible session shape. It is not coaching, it does not know your ability or your goals, and you should never swim alone.