Yards, metres, and the eight percent that ruins swim logs
A yard is 0.9144 metres exactly, so 100 yards is 91.44 metres — a little under eight and a half percent short. Nearly every US pool is 25 yards; nearly every published time standard outside the US is metric; and pool clocks do not care which. The result is a lot of swim logs where a season of improvement is actually a change of venue.
| Pool | Lengths for 1,000 yd | Lengths for 1,000 m | Lengths for a swim mile |
|---|---|---|---|
| 25 yd | 40 | 43.7 | 66 (1,650 yd) |
| 25 m | 36.6 | 40 | 60 (1,500 m) |
| 50 m | 18.3 | 20 | 30 (1,500 m) |
Note that the "swim mile" is a piece of vocabulary, not a mile. The 1,650 yard freestyle is the standard US distance event and is 1,509 metres; the 1,500 metre is 1,640 yards. A statute mile is 1,760 yards, so both events are short of one. If you are logging distance for a triathlon or an open water goal, log the actual yardage and convert once, at the end.
What pace per 100 is for
Held constant it is a fitness measure, but its real use is structuring a set. Interval sets are written on a send-off — 10 x 100 on 2:00 means you leave the wall every two minutes and your rest is whatever is left after you swim. Knowing your honest repeat pace is what makes the send-off produce the intended rest rather than a set that quietly becomes continuous swimming or one you fail in the sixth repeat. A common construction is a base pace with ten to twenty seconds of rest, which for a 1:45 per 100 swimmer means 100s on 2:00, not on 1:45.
The other reason to track it is that it exposes what the clock on the wall hides. Total pool time and swimming time diverge fast: an hour-long session with a warmup, a drill set with fins, and conversation at the wall may contain twenty-five minutes of actual swimming. Enter only the swimming time if you want the pace to mean anything.
Getting faster is mostly not about turnover
Swimming speed decomposes into stroke rate multiplied by distance per stroke. In untrained swimmers the second term is doing far more of the work and has far more room in it, because water resistance rises with roughly the square of velocity and a poor body position adds drag that no amount of arm speed pays for. The practical measurement is stroke count per length: count strokes over a 25 at your normal effort. For an adult recreational swimmer, high teens to about twenty per 25 yards is reasonable, and consistently over twenty-five is a signal that body position and the catch, not conditioning, are the limiting factor.
Which is why the pace bands compress at the fast end. Going from 2:30 to 1:50 per 100 is mostly aerobic fitness and comfort in the water and arrives in months. Going from 1:30 to 1:20 is technical, requires eyes on your stroke that are not your own, and can take a season or several.
The calorie figure and why it is soft
The estimate uses the MET method: kilocalories per minute equal MET times 3.5 times body mass in kilograms divided by 200, with MET values drawn from the 2011 Compendium of Physical Activities. Freestyle appears there at 5.8 for slow, 8.3 for moderate and 9.8 for vigorous, and other strokes differ substantially — breaststroke ranges roughly 5.3 to 10.3, butterfly is listed near 13.8. Those are averages across studied groups, not measurements of you.
Swimming has a specific reason to be cautious with the number. Efficiency varies enormously between swimmers, more than in running or cycling, because a struggling swimmer is fighting drag that a smooth one has eliminated — two people covering the same distance in the same time can differ considerably in energy cost. And the figure is gross: it includes the resting metabolism you would have spent anyway. The row labelled "above resting" strips that out, and for moderate freestyle it removes about twelve percent.
Questions people ask
Do I count lengths or laps?
This page counts lengths — wall to wall, one direction. That is the convention in competitive swimming and on most pool clocks. "Lap" is used both ways in casual speech and means a round trip in running, so if you counted round trips, double your number before entering it. Twenty round trips of a 25 yard pool is 40 lengths and 1,000 yards.
How do I convert a 100 yard time to 100 metres?
Multiply by 1.0936, which is the reciprocal of 0.9144. A 1:30 per 100 yards is 1:38.4 per 100 metres; a 1:15 is 1:22.0. Going the other way, multiply the metric time by 0.9144. This is a pure distance conversion and assumes identical speed, which is close enough for training logs. For race times the conversion is messier because a 25 yard course gives you more turns and more underwater per unit distance than a 50 metre course, and turns are faster than swimming — which is why official conversions between short course yards, short course metres and long course metres apply an additional time adjustment rather than just the length ratio.
Is swimming good for weight loss?
It burns comparably to running per unit time at matched effort and is far kinder to knees, ankles and hips, which makes it the obvious aerobic choice for anyone carrying injury or extra weight. The complication that keeps coming up in the literature is appetite: water conducts heat away from the body far faster than air, and cold-water exercise has been observed to increase subsequent food intake in ways that land exercise does not. This does not make swimming ineffective; it makes the calorie number on this page a poor basis for eating decisions. Track intake separately from output.
Why is the pace worse than my watch says?
Wrist swim tracking counts lengths by detecting turns and estimates stroke type from motion, and it drops or adds lengths when you push off softly, do a drill with fins, or stop mid-length. It also usually times the whole session including rest, or the whole session excluding it, depending on settings — and those give very different paces. If the two disagree, count a set by hand and check which one moved.