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I've been swimming off and on for years, but recently I've begun to wonder about the number of calories I expend while swimming so I can compare it with other activities.

The calculators I've found so far exclusively ask about the time spent and the stroke (and perhaps gender, age, height, and weight). This seems totally incorrect to me, but who am I to question so many experts? Still, let me ask the question.

My problem is that I swim slowly. I saw someone at the pool today swim at least 5 laps for every lap of mine. So he is burning a lot more calories per minute than I am, but he and I would show up as burning the same amount in these calculators (assuming the same stroke and roughly the same body size).

It seems to me that it would be much more accurate to base the number of calories on the distance rather than time spent swimming, because the effort is expended to move your body through the water. If I go 1200 meters in 45 minutes, am I really burning that many more calories than someone going 1200 meters in 15 minutes? 'Cause I'm sure getting credit for a lot more when I swim slowly.

Does anyone know why most calorie calculators use time rather than distance (or both), and whether any of them are reliable?

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  • Welcome to Sports Stack Exchange. Can you clarify whether you are talking about competitive swimming or general fitness/exercise swimming?
    – Nij
    Commented Feb 21, 2021 at 2:34
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    If you compared your running speed to someone else's running speed, and theirs was higher, they would indeed be burning more calories. But it's different in water, because what matters is how much water you displace per unit time. And with dreadful technique, the slowest swimmer can easily burn more calories. Hell, I could stand still and flail around against the resistance of water and burn lots of calories.
    – Alec
    Commented Feb 22, 2021 at 17:13
  • Also consider that a large portion of swimming faster is form based, which also means the better your form, the more efficient you are, which equals less calories expended.
    – JohnP ♦
    Commented Feb 22, 2021 at 18:59
  • @Alec - And that is the essence of deep water aerobics :)
    – JohnP ♦
    Commented Feb 22, 2021 at 19:13

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The speed at which you travel doesn't matter much. What matters is how hard you are exerting yourself! If you're hitting a 180 heart rate, then you're burning a similar amount to what someone else hitting a 180 heart rate is burning, no matter what their speed is.

See this article for example; they talk about "fast swimming", but what they mean by that is "fast for you", which takes a higher heart rate.

A good comparison might be my wife and I running. I run a lot faster than she does - I do a 5k in under 25 minutes, while she does a 5k in 45 minutes. But we're both hitting relatively high heart rate - a little higher on my end, because I'm more competitive, so maybe I'm doing 180 for those 5k, while she's doing 170. Still, she burns a lot more calories - because she's keeping up that high-ish heart rate for almost twice as long.

It's entirely possible that some of the "fast" swimmers are burning less than you, both if they are more fit (so their heart rates are much, much lower), slimmer and/or lighter (less drag!), and if their form is much better (again, much less drag).

Ultimately, what you should focus on is your weight, your heart rate, and the time - nearly everything else is irrelevant, from a calorie-burning perspective.

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  • This is not entirely correct. Calorie burn is a function of oxygen consumption. Often higher heart rates accompany higher exertion/breathing, so it can be confused. If you are sitting on the couch and have a HR 10 beats higher than yd sitting on the couch, you really aren't burning more calories (Other than the miniscule amount for the extra muscle work). Also, calories for running are almost purely a function of weight and distance A 200 lb person that goes 1 km in 45 minutes will burn the same calories as they would if they did 1 km in 15 minutes.
    – JohnP ♦
    Commented Feb 22, 2021 at 18:56
  • Hm, I think while you're technically correct in the first part, this is a good generalization for a layman in terms of things they can measure, though I'll happily delete if a better answer that is technically completely correct comes along. And I don't agree with the last sentence, though I think you don't quite have it worded right - if I ran 5km in 45 minutes, I'll certainly be using more oxygen than I would running (well, walking) 1km in that time; but if that's my normal running speed, then I would agree.
    – Joe
    Commented Feb 22, 2021 at 19:02
  • That makes more sense, but I still disagree. The major factors are time and body weight, but effort does matter in calories burned - it might be 150 calories versus 140, but you do burn more calories when you run/swim/etc. faster compared to yourself running/swimming slower (just comparing you to yourself). What doesn't compare is two different people - it might take more calories for me to go 5km/25m than for you to go 6km/25m, for identical body weights, or more for you, or same, just depending on various factors.
    – Joe
    Commented Feb 22, 2021 at 22:02
  • Joe - This is what I get for commenting while tired and sick. For a single individual, weight and distance are the factors. If I (180 lbs) complete a 5k, the calories will be basically the same whether I do it in 15 minutes or 30 minutes.
    – JohnP ♦
    Commented Feb 22, 2021 at 22:16
  • Guys, this looks like an interesting disagreement. Are there any mediators who can help resolve it? I'm inclined to think that I'm going to burn roughly the same number of calories when I swim 1200 meters, whether I'm doing it in 45 minutes or 15 minutes. But I do see how a lot of factors enter into it, like body size/shape and stroke efficiency. I don't quite get why relative fitness is a factor. Sounds like it would be difficult to come up with a really accurate number.
    – vknowles
    Commented Feb 22, 2021 at 23:35

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