Swimming Pace Calculator
Find your pace per 100 m or 100 yd, the time for any swim, splits, and your critical swim speed (CSS) with training paces from a 400 and a 200.
How to Use
- Choose Pace to get pace per 100 from a swim you did, Swim time to plan a swim at a pace, or CSS test for your critical swim speed.
- Enter the distance in metres, yards, km or miles, and the time as h:mm:ss or m:ss (a plain number counts as minutes).
- Pick whether pace is per 100 m or per 100 yd; the other one is always shown too, converted with 1 yd = 0.9144 m exactly.
- For CSS, swim an all-out 400 and, after a full rest, an all-out 200 in the same pool, and enter both times.
- Read the pace, splits or CSS training bands, and check Show Work for each conversion.
Worked Example
Pace from a swim. 1500 m in 30:00 is 1,800 s over 15 hundreds: 1,800 ÷ 15 = 120 s, or 2:00 per 100 m. In yards: 120 × 0.9144 = 109.7 s, so 1:49.7 per 100 yd, and the 1500 m is 1,500 ÷ 0.9144 = 1,640.4 yd.
Critical swim speed from a 400 and a 200. A swimmer does an all-out 400 m in 6:00 (360 s) and, after a full rest, a 200 m in 2:50 (170 s). CSS = (400 − 200) ÷ (360 − 170) = 200 ÷ 190 = 1.053 m/s, which is (360 − 170) ÷ 2 = 95 s, 1:35 per 100 m. Endurance sets at CSS + 6 to 10 s go at 1:41–1:45; threshold repeats at 1:34–1:37.
The common mistake: using the 400 pace as the threshold pace. 6:00 for 400 m is 1:30 per 100 m, and it is tempting to train at that. But a single all-out 400 is faster than a pace that can be repeated set after set; CSS, the slope between the 200 and the 400, lands at 1:35, 5 s per 100 slower. Training threshold sets at 1:30 would turn them into all-out efforts.
Show Work
Formulas
Where Critical Swim Speed Comes From
The idea of a “critical” work rate that can in theory be held indefinitely goes back to the critical-power model of Monod and Scherrer in the 1960s. In 1992 K. Wakayoshi and colleagues applied it to swimming in “A simple method for determining critical speed as swimming fatigue threshold in competitive swimming” (International Journal of Sports Medicine, 13(5): 367–371). Eight highly trained swimmers swam to exhaustion at set speeds in a swimming flume and at maximal effort over four distances in a pool; plotting distance against time gave straight lines, D = a + b × T, with r² above 0.998, and the slope b is the critical speed.
Their follow-up in the European Journal of Applied Physiology (1993) asked whether critical swimming velocity matches the intensity at maximal lactate steady state. Coaches simplified the test to just two swims, a 400 and a 200, which gives the slope directly as (400 − 200) ÷ (T400 − T200) — the form used by TrainingPeaks and most triathlon coaches today.
Pools come in metres and yards. Since the 1959 international agreement a yard has been exactly 0.9144 m, so a 25-yard pool is 22.86 m and every yard pace converts to metres by dividing by 0.9144.
About This Tool
This calculator works in metres and yards side by side: give it a distance and time for your pace per 100, or a pace for the time, and it lists the splits at 25, 50, 100 or 200. The CSS mode turns an all-out 400 and 200 into your critical swim speed, plots the two swims with the line whose slope is CSS, and sets training bands around it — bands that follow a common coaching convention, so adjust them to how the sets feel.
Everything runs in your browser; nothing you enter is sent anywhere. For general information only — not medical advice. Talk to a doctor or other qualified professional about your own health.
Related tools: Running Pace Calculator, Cycling Power Zones & W/kg Calculator, and Rowing Split & Watts Calculator.
Frequently Asked Questions
How do I calculate my swimming pace per 100 m?
Divide the time in seconds by the distance in hundreds of metres. 1500 m in 30:00 is 1,800 s ÷ 15 = 120 s, so 2:00 per 100 m. In a 25-yard pool the same speed is 1:49.7 per 100 yd.
How do I convert pace per 100 yards to per 100 metres?
A yard is exactly 0.9144 m, so 100 m takes 1 ÷ 0.9144 = 1.0936 times as long as 100 yd. A pace of 1:40 per 100 yd (100 s) is 100 ÷ 0.9144 = 109.4 s, or 1:49.4 per 100 m.
What is critical swim speed (CSS) and how do I work it out?
CSS is the speed you could in theory hold for a long time without tiring, taken as the slope of distance against time. From an all-out 400 and 200 it is 200 ÷ (T400 − T200), or as a pace per 100: (T400 − T200) ÷ 2. A 400 in 6:00 and a 200 in 2:50 give (360 − 170) ÷ 2 = 95 s, which is 1:35 per 100 m.
What training paces come from my CSS?
A common convention sets bands as seconds per 100 either side of CSS. With a CSS of 1:35 per 100 m: endurance at CSS + 6 to 10 s is 1:41–1:45, threshold at CSS − 1 to + 2 s is 1:34–1:37, and speed work at CSS − 2 to − 5 s is 1:30–1:33. They are starting points, not a published standard.
How long would a 1500 m swim take at my CSS?
Multiply the CSS pace by 15. At 1:35 per 100 m that is 15 × 95 = 1,425 s, or 23:45. That assumes an even pace exactly at CSS the whole way; a real race will differ.
How do I use the Swimming Pace Calculator?
Simply type your numbers and read the result, which refreshes the instant you change something. There is nothing to submit and nothing to wait for.
Do I need to install or sign up for anything?
Not at all — it runs in the browser with nothing to install and no account. After it loads once, it even works without an internet connection.
Is my information private?
Yes. Everything happens in your browser. Nothing you type is sent to a server or saved anywhere.
Common Use Cases
Triathlon swim pacing
An Ironman swim of 3.8 km in 1:15:00 is 1:58.4 per 100 m (1:48.3 per 100 yd).
Yard pool to metric
500 yd in 8:20 is 1:40 per 100 yd, which is 1:49.4 per 100 m — not 1:40.
Planning a set
A 400 m at 1:45 per 100 m takes 7:00, with each 100 at 1:45.
Setting threshold sets
A 6:00 400 and a 2:50 200 give a CSS of 1:35; threshold repeats go at 1:34–1:37 per 100 m.
Open-water splits
1500 m at 2:00 per 100 m passes 500 m at 10:00 and 1000 m at 20:00, finishing in 30:00.
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