Concepts

Stroke length is the distance your body travels forward on each arm stroke. How far you travel on each stroke is a direct indicator of how much work you accomplish and that work is a product of both strength and skill. Some people get more from their strength and others more from their skill while the best get it from a proportional amount of both. 

You could go farther per stroke mostly by strength but that is an energy-expensive way to do it and one that puts more strain on the body.  Eventually, you reach exhaustion or injury trying to shove water out of the way like a bulldozer. 

You could go farther per stroke mostly by skill but you’ll go slower and slower doing it. You cannot avoid the fact that even with the most streamlined and coordinated body, you have to move out of the way the same mass of water as your body mass. Shape creates the knife-like vessel but you still have to use strength to push that knife into the water ahead. 

The more strength you can bring to bear behind your skill, the more momentum you can build up and ride, requiring less energy to maintain once you get up to speed. A strong body generates force, and a skilled body transmits that force and extends its productivity. 

The swimmer that over-emphasizes perfection in technique must be willing to work harder in such a way that some failure is encountered in their practice because it is failure that reveals where the technical weak spots are, and thus points to where more effort needs to be applied. By this, the swimmer builds strength around that specific skill so that it holds under harder swimming. 

The swimmer that over-emphasizes strength must be willing to slow down movements in order to train them to be more skillful. The body under fatigue or distraction will prefer the dominant or neurologically ‘easier-to-execute’ movement pattern, and the swimmer must spend enough time under easier conditions making the superior movement pattern the more dominant one so that they can maintain it under difficult conditions and fatigue.

The general approach to developing both is to acquire a set of streamline and coordination skills, then put those to work in more challenging sets (more intensity, and/or more continuous distance) so that you build up strength around those skills. You build strength around those skills (rather than just building unskilled strength) when you maintain a skill standard while doing the harder work. When you disregard the standards while doing the harder work, you end up with two different stroke patterns – a skillful one that shows up only under gentle swimming and an unskillful one that emerges when the going gets tough. 

Calculations

Stroke length = swim distance (in the pool where you are actually taking strokes, not gliding) / the number of strokes you take in that distance

Counting strokes gives you a number that makes sense to you individually in the pool length you normally swim in – you can compare your work from one length to another, and from one practice set to another. By converting that number into stroke length, you now have a number that you can use to estimate your stroke count in other pool lengths and to make more comparisons, such as getting a sense of how you are developing compared to other swimmers. 

[This following section has been updated to correct the first paragraph’s explanation and add the second paragraph.]

Take your stroke length and divide by your height (or better, by your wingspan) – this produces a number that tells you how much of your body or wingspan length forward you travel on each stroke – which will almost certainly be a decimal or percent less than 1.00 because traveling a full body length would be 1.00 and that would be impractical if not impossible for most. A result of >0.70 would be exceptional, even elite (if you were also going very fast). A result of around 0.60 would be admirable, above average, though it doesn’t tell what balance of skill and strength is achieving that. A result of around 0.55 may be about average among developed swimmers. A result of <0.50 would suggest a need for more development in skill and/or strength. 

Here is one more interesting data point that should influence the expectation you have for your stroke length. Statistically, the heights of humans are just about the same as their wingspans, give or take 5%. We say that using your height is good enough for initially setting your expectation of stroke length. However, you are using the arms to lever against the water, and that 5% difference in wingspan length compared to the torso can have an impact on how far you can travel forward. The Wingspan Coefficient (WC) is the number produced by taking your wingspan and dividing it by your height. If your WC number is somewhere between 0.98 and 1.02, that could be regarded as an average WC and a decent stroke length for a developed swimmer of your dimensions maybe around 0.55. If your WC number is below 0.98 then your arms are short relative to your height and a decent stroke length may be a bit less than 0.55. If your WC number is above 1.02 then your arms are long relative to your height and a decent stroke length may be a bit more than 0.55. 

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