Swimming calculators
Four tools, no sign-up, nothing stored. Each one shows the formula it uses and links the source it came from, because a number you cannot check is a number you should not train against.
Critical Swim Speed
Two time trials give you your threshold pace and five training zones in seconds per 100.
Swim pace
Distance and time in; pace per 100, speed in m/s and the full split table out.
Course converter
SCY, SCM and LCM both ways, with the distance-only and seeding-factor answers side by side.
SWOLF
Efficiency score plus distance per stroke, and the caveats that make it usable.
Which one answers your question
| Use this | When |
|---|---|
| Critical Swim Speed | You want a number to write sets against instead of guessing at effort. |
| Swim pace | You have a target time and want to know what the clock should read at each split. |
| Course converter | You swam in one pool and need the time in another — for an entry, or to compare fairly. |
| SWOLF | You want to know whether a faster swim came from better technique or just more effort. |
How they fit together
They are meant to be used in a sequence, not in isolation. Swim a time trial and put it through the pace calculator to see where you are. Run the CSS test to turn that into training zones. Use the SWOLF calculator every few weeks to check that the improvement is coming from the stroke and not only from working harder. And if you change pools, put everything through the course converter first, because none of these numbers travel between a 25 m and a 50 m pool unchanged.
What the calculators cannot do is tell you what to fix. When the numbers say the stroke is the limit, the technique section is where to go; when they say fitness is the limit, the workouts section has the sets.
Why we show the working
Most swimming calculators are a form and a result. That is fine until the result surprises you, at which point you have no way to tell whether the tool is wrong, your input is wrong, or your assumption is wrong. Every calculator here prints the formula, names the study or governing body behind it, and — in the case of course conversion — shows two different methods rather than pretending there is one right answer.
Frequently asked questions
Are these calculators free?
Yes, all of them, with no account and no email. They run entirely in your browser — nothing you type is sent anywhere or stored.
Which calculator should I start with?
The pace calculator if you just want to make sense of a time you already swam, and the CSS test if you want to start training to a number. SWOLF is worth adding once you are training regularly and want to know whether your technique is improving or just your fitness.
Do these work in yards?
The pace calculator takes yards or metres directly, and the course converter exists precisely to move between them. For CSS and SWOLF, run the test in whichever unit your pool uses and read the result in that unit — just do not mix the two between sessions.
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.