Converting Swim Times: Everything You Ever Wanted To Know

Converting Swim Times

Swimming is a fun and family-friendly sport. Yet, one topic that invariably trips up new swim moms and dads is the concept of “swim courses” like “SCY” and “SCM” and understanding why and how times are converted between them. In this post, we explain all the acronyms and jargon, and dispel the mysteries and common misunderstandings around converting a swim time from one course to another.

What is a swim course?

Simply put, “swim course” is just a fancy name for a standard pool length. In the US, there are three commonly encountered lengths, or courses, for competition pools. They are:

  • 25 yards — also known as “short course yards” or simply “yards”. This pool length is frequently used for year-round/club, high school, and collegiate competitions, and is also often used for neighborhood and country club pools. This course is abbreviated as “SCY” or just “Y”.
  • 25 meters — also known as “short course meters” or simply “short course” or “meters”. This pool length is generally used for international competition and is also used for some neighborhood and country club pools. This course is abbreviated as “SCM” or just “S”.
  • 50 meters — known as “long course meters” or simply “long course”. This is the pool length used for the Olympics and many international competitions, and during the “long course season” of USA Swimming from April to August. This much larger pool size is rarely used for neighborhood or club pools. This course is abbreviated as “LCM” or just “L”.

The diagram below shows the relative lengths of each of the standard courses:

Relative lengths of 25 yard (short course yards), 25 meter (short course meters) and 50 meter (long course meters) pools

The key thing to remember about swim courses is that they describe different distances. A 25-yard pool is equivalent to 22.86 meters, or a bit more than 90% the length of a 25-meter pool. And, of course, a 50-meter pool is twice the length of a 25-meter pool.

Side note: accounting for imprecise pool lengths
It is not uncommon for recreational pools to not be built to exacting standards. When measured precisely, many neighborhood pools will be a little longer or a little shorter than their specified course. In some cases, such as 20-yard or 33 ⅓ yard pools, the difference can be very significant. To account for these variations, sometimes a pool-specific “course correction factor” is calculated and applied to all results recorded in that pool. This course correction is similar to, but different from, the time conversion used to estimate times between standard pool courses. These course correction factors, if used, are calculated and tracked separately for each pool.

Diving in

What is time conversion?

The vast majority of Summer league swim meets are held in either a 25-yard or 25-meter pool. It is common in Summer league swimming to swim in a “yards” pool one week, and then in a “meters” pool the next. With some times recorded in “yards” pools and others from “meters” pools, they can’t be compared and used as-is for meet seeding and other purposes. This is where time conversion comes in: it allows times recorded in pools of different lengths (aka courses) to be used interchangeably for seeding, meet qualification, and other purposes.

The most important thing to remember is: all time conversions are estimates, not exact calculations. Unlike conversion from one distance to another, which is precise, a time conversion estimates the time it would take a swimmer to swim a specific distance based on that swimmer’s previous time swimming the same stroke over a different distance. 

converting times

Converting Swim Times From Yards to Meters

Let’s illustrate with an example. If Susie swam a 50-yard breastroke in a 25-yard pool in 34.45 seconds, approximately how fast would Susie swim a 50-meter breaststroke in a 25-meter pool?

One yard is equivalent to 1.0936 meters, thus 50 yards is exactly equivalent to 45.72 meters.

If we simply multiply Susie’s 34.45 time by the distance conversion factor (1.0936), we would get an estimate of 37.67 seconds. Converting this way is not very accurate, however, because it just converts the distance—it doesn’t take into account the fact that Susie would be swimming a longer distance, and that is likely to affect her overall pace. 

As the distance increases, it’s a safe bet Susie’s pace will gradually get slower. In the same way we wouldn’t expect Susie to hold her 25 sprint pace for a 200, we should expect the difference in distance in this example (4.28 meters) to have some small but measurable impact on Susie’s overall pace. That impact should be reflected in the converted time estimate.

To precisely estimate how this extra distance would affect Susie’s converted time, we’d need to know more about Susie. Some swimmers are sprinters, and others excel at distance events. Depending on athletic ability, age and other factors, the impact of a change in distance will have on an athlete’s time can vary significantly from swimmer to swimmer. Taking into account all those factors would add a lot of complexity.

In practice, for the sake of simplicity, a standard conversion factor of 1.11 has traditionally been used by most swim software, including SwimTopia, when converting 25-yard times to 25-meter times (and vice versa). This conversion factor includes the distance conversion (1.0936) plus a little extra (0.0164) to account for the impact of the extra distance on the overall pace. The difference in distance between 25-meters and 25-yards is close enough that applying more complex conversion techniques would not yield significantly better estimates—or at least not enough to justify the additional complexity.

Using this standard “simple” conversion factor, Susie’s 34.45Y (short course yards) time would convert a 38.24S (short course meters) time. In this example, the course abbreviation is appended to the time to let you know what course the time was recorded in.

Keep in mind this converted 38.24S time is just an estimate. Depending on the swimmer and conditions of the swim, the converted estimate might be spot on or way off compared to an actual timed swim in the target course. In general, most of the time, it will be pretty close, and that makes it a useful, simple approximation.

Side note: rounding converted times

When converting swim times between courses, one will often end up with extra digits that need to be rounded to hundredths of seconds. Rather than using simple rounding rules, most swim software, including SwimTopia, use a more complex rounding technique known as “statistician’s rounding” or “banker’s rounding.” This approach reduces bias by only rounding up from 0.5 when the previous digit is odd. Thus a time of 23.435 would round up to 23.44 and a time of 23.445 would round down to the same 23.44.

More Complex Time Conversions

converting swim times - swimmersWhile converting short course yards (25yd) to short course meters (25m) is relatively simple, converting between short course (25m) and long course meters (50m) adds an extra twist: estimating the impact of the turn (or lack thereof) on the time.

Things get even more interesting when converting times for longer distance events. For example, converting a 1,650-yard time to a 1,500-meter time. In this case, the number of turns and the distance will be quite different. 

There are many different approaches to converting swim times. This is why you’ll often get different results when converting times using the various swim time conversion tools you can find on the web. 

A common simple conversion calls for adding 2% when converting from short course to long course to account for fewer turns. However, the differences in turning speed for different strokes and athletes are significant enough that more complex conversion methods are usually warranted.

The more accurate conversion methods rely on statistical analysis of large samples of swim times to calculate tables of conversion factors for every combination of age, gender, stroke and distance. All of those factors (age, gender, stroke and distance) will be taken into account when estimating a converted time using this method.

While some approaches may be more accurate than others, no conversion method is perfect or absolutely correct. At the end of the day, all conversions are still just estimates. Two swimmers of the same age and gender swimming the same stroke and distance will each have different strengths and weaknesses that cannot be distilled to a single formula. The only way to really know how fast a swimmer is going to swim, is for that swimmer to prove it in the pool.