How to use it
- Type the Distance swum and choose the Distance unit: metres or yards.
- Enter the Time for that distance, for example 3:00 for 200 m.
- For critical swim speed, add the 400 m time and the 200 m time from two all-out swims. Leave both empty if you do not have them.
- Read Pace and Critical swim speed pace, then open Training paces from your CSS pace and the table of times at common distances.
How the pace is calculated
Pace is the time taken for 100 units of the distance. The pace per 100 m is the time multiplied by 100 and divided by the distance in metres. A yard is exactly 0.9144 m, so the pace per 100 yd is the time for 91.44 m, multiplied by 100 and divided by the distance in metres.
Pace per 100 m = time (s) × 100 ÷ distance (m)
Pace per 100 yd = time (s) × 100 × 0.9144 ÷ distance (m)
Speed (km/h) = distance (m) ÷ time (s) × 3.6- Pace is shown as minutes and seconds, rounded to the whole second.
- Times with hours are shown as h:mm:ss.
Critical swim speed
Critical swim speed (CSS) is found from two maximal swims, a 400 m and a 200 m. Wakayoshi and colleagues (1993) took critical velocity as the slope between the times for 200 m and 400 m, and found that it correlated with the swimming speed at 4 mmol/l blood lactate and with the mean 400 m speed. They suggested it may match the intensity of maximal lactate steady state.
CSS (m/s) = (400 − 200) ÷ (time for 400 m − time for 200 m)
CSS pace per 100 m = (time for 400 m − time for 200 m) ÷ 2
Example: 6:10 for 400 m (370 s) and 2:56 for 200 m (176 s): (370 − 176) ÷ 2 = 97 s, which is 1:37 per 100 m.- Both swims must be all-out, because the formula assumes maximal effort.
- Critical swim speed is an estimate from two swims, not a measured laboratory value.
Training paces from critical swim speed
Training zones are percentages of your CSS pace. Because the percentage applies to the time per 100 m, a higher percentage gives a slower pace. The five zones and their purposes follow one coaching article: Z1 aerobic for warm-up and long distances, Z2 endurance for continuous swimming, Z3 CSS for the main set, Z4 VO2 for high-intensity intervals and Z5 sprint for 50 to 100 m all-out. Other coaches use other percentages.
Zone pace per 100 m = CSS pace × zone percentage ÷ 100
Example: CSS pace 97 s; Zone 2 at 105 to 110%: 97 × 105 ÷ 100 = 101.85 s and 97 × 110 ÷ 100 = 106.7 s, which is 1:42 to 1:47 per 100 m.- Each pace is rounded to the whole second, as the rest of the page is.
- Zone 5 has no faster limit: it is every pace faster than 95% of the CSS pace.
What this does not cover
- Turns, starts and stroke. The times over short distances include them, so the pace per 100 m is only an average.
- Other training systems. The zone percentages come from one coaching article, and one coaching page measures CSS with a 50 m and a 400 m swim instead of a 400 m and a 200 m swim.
Worked example: 200 m in 3:00, with a 400 m of 6:10 and a 200 m of 2:56
3:00 is 180 seconds. The pace is 180 × 100 ÷ 200 = 90 seconds, which is 1:30 per 100 m. Per 100 yd it is 180 × 100 × 0.9144 ÷ 200 = 82.3 seconds, or 1:22.
The speed is 200 ÷ 180 × 3.6 = 4.0 km/h. The critical swim speed is 200 ÷ (370 − 176) = 1.03 m/s, and the CSS pace is (370 − 176) ÷ 2 = 97 seconds, or 1:37 per 100 m.
Zone 2 (endurance) is 105 to 110% of the CSS pace: 97 × 105 ÷ 100 = 101.85 seconds and 97 × 110 ÷ 100 = 106.7 seconds, which is 1:42 to 1:47 per 100 m.
| Distance | Time at 1:30 per 100 m |
|---|---|
| 50 m | 0:45 |
| 100 m | 1:30 |
| 400 m | 6:00 |
| 1,500 m | 22:30 |
Frequently asked questions
How is pace per 100 m different from speed?
Pace is the time taken to swim 100 metres, so a lower number is faster. Speed is the distance covered in an hour, so a higher number is faster. The tool shows both, with the speed in kilometres per hour.
Why does the tool show pace per 100 yards as well?
Pools in the United States and some other countries are measured in yards, and coaches there often write sets per 100 yd. The tool converts between the two units using the exact length of a yard, 0.9144 m.
Do I need a 400 m and a 200 m time to use it?
No. Pace and speed need only one distance and one time. The critical swim speed needs both the 400 m and the 200 m time from all-out swims.
How accurate is the critical swim speed?
It is an estimate from two swims, not a laboratory measurement. Use it to set training pace and to check your progress over time.
Why must the 200 m be swum all-out?
The formula assumes both swims are maximal efforts, so a swim held back gives a wrong value and a wrong training pace.
What do the training zone percentages mean?
Each percentage is a share of your CSS pace per 100 m. Zone 1 at 110 to 115% is 10 to 15% slower than your CSS pace, so it suits warm-ups and long, easy swims; Zone 5 is under 95%, which is faster and suits all-out swims of 50 to 100 m.
Does the tool keep my times?
No. Everything is worked out in your browser, and nothing you enter is sent to us or saved on your device.
Sources
- Wakayoshi K, Yoshida T, Udo M, Harada T, Moritani T, Mutoh Y, Miyashita M (1993): Does critical swimming velocity represent exercise intensity at maximal lactate steady state?, European Journal of Applied Physiology 66(1): 90-95 (abstract record; 200 m and 400 m maximal swims)
- MyProCoach: Critical Swim Speed, the 400 m and 200 m method (CSS pace = (400 m time - 200 m time) ÷ 2)
- Understanding CSS Critical Speed: The Science Behind Swim Interval Training (article with the Z1 to Z5 zone table, pace as a percentage of CSS pace)
Figures and text last checked on Tuesday, November 10, 2026.