On Swimming and Running: How Long a Run Is Equivalent to a 10 Mile Swim?

I know a lot of runners. They like to talk about running. That’s fine with me; I like to learn new things, even if I’m never going to use them. Sometimes they like to tell me how much they hate swimming, and that’s fine with me too, although I’m not really sure what to say about it. I don’t hate running. I just don’t see much point in it. There’s too much sweating and too much gravity.

Sometimes I run in order to get into water so I can swim. I don't think I look like these guys. Photo from Two Point Pictures.
Sometimes I run in order to get into water so I can swim. I don’t look like this. Photo from Two Point Pictures.

But recently a runner asked me about my upcoming swim, and when I said it was 10 miles, he said, “That’s like a 100 mile run!” I don’t think that’s true, but it made me wonder about equivalencies between running and swimming distances.

You certainly can’t make comparisons based on the proportions of swim to bike to run in a triathlon. The reason there is a 2.4 mile swim in the Ironman triathlons is not because someone thought 2.4 miles swimming is equivalent to 26.2 miles running; it’s because 2.4 miles is the distance of the Waikiki Roughwater Swim, the water portion of the original Ironman, and 26.2 miles is the distance Pheidippides ran from Marathon to Athens (and died. “Why couldn’t Pheidippides have died here?” Frank Shorter reportedly said to Kenny Moore at the 16-mile mark of one of Shorter’s first marathons).

The swim section of a triathlon takes much less time than the other two sections. At the Ironman distance, according to their world championship rules, you have 2 hours 20 minutes to do the swim, 10 hours 30 to finish the bike section (that is, swim time plus bike time), and 17 hours to finish the whole race. And even so, that 2:20 cut off for the swim portion seems alarming long to me: if it takes someone that long to swim 2.4 miles, either the conditions are very poor or the person has very low levels of swimming competency. They give you 6:30 (more even, if you come in before 10:30 on the bike) for the 26.2 mile run, but you can sit down in the middle of a run to rest for 30 minutes and not sink beneath the waves never to be seen again.

The proportions are similarly disproportionate for shorter triathlons too: I see advertisements for events that are 500m swims, followed by 20K bike rides and 5K runs.

We could use time as a way of calculating the equivalent running distance to a 10 mile swim. I swim 30-minute miles, more or less. I can swim faster (I did 54 minutes and change for a 2 mile race in a lake last August; I can swim 4000 yards in an hour at top speed in a pool), but on long open water distances I have to factor in time for eating and navigating (cough getting lost cough) and whatnot. There are three waves scheduled for the 10-mile race in July, based on estimated time — less than 5 hours, 5 to 6 hours, and more than 6 hours — and I seeded myself in the middle one. I’m unlikely to swim it faster than 5 hours, but I will be a little disappointed if it takes 6.

So, however far a person can in run 5+ hours, maybe that’s equivalent to a 10 mile swim? How far is that? Or do you think there is a better way to compare swimming and running?

Part of the reason I know so many runners is that there are a lot of runners in the world, but another part is that FIRST: Furman Institute of Running and Scientific Training is based at my university. I know these guys — they’re great people — and if you run, you need to check them out: they have a book and training programs, and they can help you be even more fantastic than you already are. None of the faculty has ever told me how much they hate swimming.

16 thoughts on “On Swimming and Running: How Long a Run Is Equivalent to a 10 Mile Swim?

  1. My understanding is that they talk about swimming as being four times *harder* than running (in terms of calorie burn etc I think), so multiply a swim distance by four to get an equivalent run distance. Therefore a 10km swim is considered ‘marathon’ distance.
    This kind of works for me as my first ever open water 10km swim took me almost exactly as long as my first marathon.

  2. A swim marathon is 10k. This distance is used because an elite swimmer will swim 10k in similar (but now slightly faster) time to an elite runner running a full marathon (which is 40k).

  3. Joe Friel’s book, Triathlon Science puts propulsion through water at about 5% efficient, while running is about 90%. So to look at the difference you should scale your time to 100% efficiency to in both sports to see the true difference in kilometers. So, if my math is correct, a 10k run is equal to about 11k at 100% and a 1500m swim is equal to about 28k at 100%. I don’t know about you, but when I get out of the water, I feel way worse than after I run a 10k fresh. If anyone wants to correct my mat, I’d be happy to accept the results, but I think swimming is WAY harder than running just based on the efficiency difference.

    1. That’s interesting. Here at the 10 Mile Swim house, we have done the math (that is, three of us together worked on it, including the one who is taking calculus this year at school), and this way of thinking suggests that 10 miles swimming is equivalent to 180 miles running. I don’t know about that.

      1. I know, it seems incredible, but the difference is the zero impact nature of swimming verses running. Swimming just seems easier than running because if you get tired, you can just float through the water. Think how far you could run in a zero gravity environment and the efficiency comparison makes more sense.

  4. I had to stop running last June (2014) due to a couple of knee problems that seem to be un-mendable so I’ve (sort of ) reluctantly had to turn to cycling and swimming – both of which have a number of negatives for me when compared to running – so I’m still in a grieving mode and trying to get over it and I’ve not yet had the passion for swimming or cycling ignited – anyhow. I spent the last 25 years running (I’m 53 now) and up until the injury last year felt pretty happy with my fitness. Since i stopped running I’ve gone up from 85-87kg to 90-91kg. I can cycle for 4.5 hours (can’t exert very much force through right knee) and I’ve had to stop swimming breaststroke as that is murder on my knee so, for the first time in my life, I’ve had to start swimming front crawl and nothing but – I can’t manage a full mile yet – mastering the breathing is the hard part – I’ve not mastered breathing both sides but I’m having to as I think that was the cause of my shoulder pain (breathing one side only) but I’d say a mile in the pool will feel about the same as a 5 mile run but it’s taking me a lot longer to swim as I’m having to rest after almost every length – really – it’s horrible feeling so bad – I managed much longer distances for running (10-13 miles regularly) but the peak aerobic demand for swimming I find much harder – I suppose not feeling natural in the water and still having to think hard about technique and breathing is also making it hard. I’ve not yet managed to experience that same hypnotic state I used to enjoy when running but I can believe it’s there – I just have to persevere. The plan is to end up swimming in open water – I don’t like being indoors especially when the weather is fine so I’m not a fan of the gym or of swimming pools – with running I could go all year round and I’ enjoyed running at night, in the snow, in the mist and rain, in the cold and I could vary y routes at a whim and steer clear of traffic and other people – cycling and swimming can’t match up but maybe the open water swimming will give me some of that same wild lonely freedom but at the moment it’s a hard slog to get swim-fit.

    1. I hope that you can find the same joy in swimming that you found in running. One piece of advice: learn to float. Invest time in learning how to position your body in the water so that floating is effortless. It’s hard to take that time, especially if you want the exercise. But it’s absolutely worth it. You can swim miles and miles miserably and not get any happier. More distance will not help. Learning to float will help.

    2. I would strongly advise you to take swim lessons with a well qualified instructor (if you haven’t already). It will do wonders for your swimming, make it seem less like a chore, more efficient and enjoyable. I too used to run but have had to turn to swimming. I occasionally get the equivalent of ‘runners high’ in the pool.

  5. I think 1kswim equals 4k run. I have done many short and long swims and it always works out about the same. I have been doing this for over 40years. 1k run for me equals about 3k on a bike. Although I am not a great cyclist! I do though hold the world record for the longest triathlon 42k swim 2000k ride 500 k run in 17days 19 hours in 1998. It nearly killed me! Many have tried to break it but have not been successful .the last attempt was by a lady who made up her own rules!i believe all types of exercise are good for you, just get out and try!

  6. I’m an ultra runner (completed 50+ ultras including a 100 miler) who ultra swims. I swim 16K lcm (10 miles) in a little over 4 hrs. I typically run a 48K (30 mi) on the road and 40K (25 mi) on single track trail. I fuel and hydrate at a similar rate in both swimming and running. That said, swimming and running are like apples and oranges – really hard to compare. Stroke efficiency accounts significantly with speed and energy used in swimming. While running technique is important, I don’t think it matters as much in ultra running as stroke technique with ultra swimming. I’m currently training for the End-Wet 36 mile swim race in June. I use similar training methods (frequency, duration, fueling) as I would if I were training for a 100K trail race. My opinion is that ultra swimming is much more difficult physically than ultra running. For whatever reason, I don’t get the same endorphin high after a 4 hr swim as I would in a 4 hr run. It seems like there’s a lot more small muscles involved with swimming. One muscle fatigues out and you’ve tweaked your entire back for a week. Running seems to involve major muscle groups (hamstrings, quads, glutes, and calves) that seem to fatigue at a slower rate than small muscles.

  7. I have experimented with many types of physical fitness HIGHS. Namely RUNNING (PRs for males 226 pounds+ 2.5KM 11:39 3KM 13:56 5KM 22:58 8KM 39:15 and 10KM 45:53), BODYBUILDING and SWIMMING. I have concluded that the SWIMMING HIGH IS THE MOST POWERFUL.

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