Swim pace calculator
Pace per 100 yards or meters, and your critical swim speed.
Two maximal swims, the second clearly longer, with full rest between. The classic pair is 200 and 400.
For general information only — not medical advice. Talk with your doctor before starting hard training, especially if you have a heart condition or have been inactive. How we check our calculators.
Pace and critical swim speed
Pace is how long you take for each 100 yards or meters; it is the number swim sets and pace clocks are written in. Critical swim speed (CSS) goes one step further. It is a single speed found from two maximal swims of different length, and it marks roughly the boundary between effort you can sustain and effort that quickly tires you. Many swimmers use it to set interval times that are hard but not wrecking.
The formulas
Pace per 100 = 100 × time ÷ distance, in the unit you swam. To convert, 1 yard is exactly 0.9144 m. For CSS, with two maximal swims of distances D1 and D2 (D2 longer) that took T1 and T2 seconds, CSS = (D2 − D1) ÷ (T2 − T1), in meters per second; the pace per 100 is 100 divided by CSS. The line d = a + CSS × t through the two points also has an intercept a, which the page uses for the model times at the bottom.
How do I calculate swim pace per 100?
Divide your time in seconds by your distance, then multiply by 100. A 1,000-yard swim in 18:30 (1,110 seconds) is 111 seconds per 100 yards, or 1:51.0. The same swim is 2:01.4 per 100 meters, because the yard is shorter: 100 yards is 91.44 m.
How do I convert a 100-yard pace to a 100-meter pace?
Divide by 0.9144, or multiply by 1.0936. A pace of 1:30 per 100 yd equals 1:38.4 per 100 m. Going the other way, multiply a per-100-meter pace by 0.9144. Swimmers who treat the two as equal overstate their yard speed or understate their meter speed by about 9%.
What is critical swim speed (CSS)?
Critical swim speed, in the research papers critical velocity, is the speed a swimmer could in theory hold for a very long time without exhaustion. Wakayoshi and colleagues proposed it for swimming in 1992 by borrowing the idea of critical power from other sports: plot the distance covered against the time at several swim speeds, and the slope of the straight line is the critical speed. In their flume study of nine college swimmers the slopes ran from 1.062 to 1.262 m/s, with a mean of 1.166 m/s.
How do I test my CSS?
Warm up, then swim a maximal 200 and, after a full recovery, a maximal 400 (meters or yards). The calculator accepts other distances as long as the second swim is longer, but 200 and 400 m is the pair the research used. Enter both times. In a 1993 follow-up with eight swimmers, Wakayoshi and colleagues showed this two-swim shortcut gave critical speeds that correlated with the speed at a blood lactate of 4 mmol/L (r = 0.914) and with the mean speed of a 400 m freestyle (r = 0.977).
Worked example: 200 in 2:30 and 400 in 5:20
The distance difference is 200 m and the time difference 170 s, so CSS = 200 ÷ 170 = 1.176 m/s, a pace of 1:25.0 per 100 m. The line also has an intercept: 200 − 1.176 × 150 = 23.5 m, the extra distance a swimmer covers beyond what pure steady-state speed would give. The same model then says 11:00 for 800 m and 20:55 for 1,500 m. Those two times are extrapolations beyond the 200 to 400 range the method was built on, so treat them as a rough guide rather than a prediction.
What do the 98%, 100% and 102% paces mean?
In the 1993 study, eight swimmers did 4 × 400 m at 98%, 100% and 102% of their critical speed. At 100% the blood lactate stayed steady at about 3.2 mmol/L, at 98% it tended to fall, and at 102% it rose through the set. The page shows those three paces because they are the ones with published evidence behind them. Coaches use many other zone systems built on CSS, but this page does not reproduce one because the percentages vary from coach to coach.
Common mistakes
Swimming the 200 and 400 at different effort (the shorter swim must be all-out, not a warm-up). Using times from different pools or from open water, where turns and currents change the result. Entering a long swim that is too close in distance to the short one, which makes the slope very sensitive to a one-second error. Entering a 400 that is faster per 100 than the 200, which gives a negative intercept; the page flags this as a sign the times do not fit. And testing when tired, which pulls CSS down.
Limits of the method
The critical speed model comes from small studies of trained college swimmers in a flume or a pool, and CSS depends on the swim stroke and the pool length. It describes a boundary between sustainable and unsustainable effort; it is not a prediction of race time and says nothing about open-water swimming, wetsuits or fatigue over hours. The 1992 paper itself concluded only that critical velocity could serve as an index of endurance performance in competitive swimmers.
Sources and related calculators
Sources: K. Wakayoshi, K. Ikuta, T. Yoshida, M. Udo, T. Moritani, Y. Mutoh and M. Miyashita, “Determination and validity of critical velocity as an index of swimming performance in the competitive swimmer,” European Journal of Applied Physiology 64:153–157 (1992); K. Wakayoshi and others, “Does critical swimming velocity represent exercise intensity at maximal lactate steady state?,” European Journal of Applied Physiology 66:90–95 (1993). This site read the abstracts of both papers, not the full texts. Related: pace calculator (running), VDOT calculator, speed converter, calories burned calculator and target heart rate calculator.